We've searched the internet and found the largest collection of On30 Scale trains for sale is on eBay. Below are the listings for 'gauge trains'.

O S Wiseman Models Metal Engine Kits Narrow Gauge
O S Wiseman Models Metal Engine Kits Narrow Gauge
$40.00
Time Remaining: 1d 10h 40m
KATO N gauge 209 based 500 series PS28 equipped Ch Sbu Line Basic 6 Car Set 1
KATO N gauge 209 based 500 series PS28 equipped Ch Sbu Line Basic 6 Car Set 1
$277.73
Time Remaining: 1d 23h 41m
Buy It Now for only: $277.73
Kato N Gauge E231 System 0 Series Ch   S bu Line 6 Both Basic Set 10 1520 M
Kato N Gauge E231 System 0 Series Ch S bu Line 6 Both Basic Set 10 1520 M
$173.80
Time Remaining: 5d 7h
Buy It Now for only: $173.80
Kato N Gauge E231 System 0 Series Ch   S bu Line 4 Both hematopoiesis Set 1
Kato N Gauge E231 System 0 Series Ch S bu Line 4 Both hematopoiesis Set 1
$95.47
Time Remaining: 5d 7h 1m
Buy It Now for only: $95.47
Kato N Gauge Kashima Waterfront Railway 6006 Girl  apos S  Pan Danzer Speci
Kato N Gauge Kashima Waterfront Railway 6006 Girl apos S Pan Danzer Speci
$56.04
Time Remaining: 5d 19h 36m
Buy It Now for only: $56.04
Kato HO Gauge HV 21 HO Uni Track Automatic Traffic Signal S Set 3 131 Japan
Kato HO Gauge HV 21 HO Uni Track Automatic Traffic Signal S Set 3 131 Japan
$139.80
Time Remaining: 5d 19h 36m
Buy It Now for only: $139.80
N Gauge 10 1147 181 System 100 Fee Collectors Stand The Time Azusa Six car
N Gauge 10 1147 181 System 100 Fee Collectors Stand The Time Azusa Six car
$177.53
Time Remaining: 5d 19h 36m
Buy It Now for only: $177.53
Kato N Gauge Diesel Train 58 Based Non air Conditioned car Express Iide 7 Car S
Kato N Gauge Diesel Train 58 Based Non air Conditioned car Express Iide 7 Car S
$250.45
Time Remaining: 5d 19h 37m
Buy It Now for only: $250.45
KATO N gauge 251 based super view Dancer appeared during coating 10 Car Set S
KATO N gauge 251 based super view Dancer appeared during coating 10 Car Set S
$309.39
Time Remaining: 7d 21h 41m
Buy It Now for only: $309.39
Rare railway model HO gauge KATSUMI Moha 484 Kuha 481 form rail F S
Rare railway model HO gauge KATSUMI Moha 484 Kuha 481 form rail F S
$600.00
Time Remaining: 9d 12h 22m
Buy It Now for only: $600.00
Varian 0572 K7360 306 Ionization Gauge I dont think its ever been used 
Varian 0572 K7360 306 Ionization Gauge I dont think its ever been used 
$50.00
Time Remaining: 11d 12m
Buy It Now for only: $50.00
KATO N gauge 251 based super view Dancer appeared during coating 10 Car Set S
KATO N gauge 251 based super view Dancer appeared during coating 10 Car Set S
$270.39
Time Remaining: 13d 10h 5m
Buy It Now for only: $270.39
KATO N gauge E233 system 5000 series Keiyo Line through organized 6 both basic s
KATO N gauge E233 system 5000 series Keiyo Line through organized 6 both basic s
$142.28
Time Remaining: 13d 10h 5m
Buy It Now for only: $142.28
Hangman Creek Lumber Company DVD HO HOn3 S Sn3 O On3 On30 Narrow Gauge
Hangman Creek Lumber Company DVD HO HOn3 S Sn3 O On3 On30 Narrow Gauge
$28.50
Time Remaining: 20d 15h 22m
Buy It Now for only: $28.50
BTS 17143 On30 Laser Cut Narrow Gauge Cheat Run Trestle Craftsman Building
BTS 17143 On30 Laser Cut Narrow Gauge Cheat Run Trestle Craftsman Building
$37.95
Time Remaining: 20d 18h 31m
Buy It Now for only: $37.95
KATO N gauge E233 system 5000 series Keiyo Line through organized 6 both basic s
KATO N gauge E233 system 5000 series Keiyo Line through organized 6 both basic s
$140.50
Time Remaining: 23d 7h 41m
Buy It Now for only: $140.50
Narrow Gauge Through the Bush Ontarios Toronto Grey  Bruce and   Nipissing
Narrow Gauge Through the Bush Ontarios Toronto Grey Bruce and Nipissing
$48.19
Time Remaining: 25d 10h 8m
Buy It Now for only: $48.19
Cagneys Locomotive Works Miniature Railroad Supplier Narrow Gauge
Cagneys Locomotive Works Miniature Railroad Supplier Narrow Gauge
$29.65
Time Remaining: 26d 5h 16m
Buy It Now for only: $29.65
Ride the Sandy River Americas Largest Two foot Railroad Narrow Gauge
Ride the Sandy River Americas Largest Two foot Railroad Narrow Gauge
$48.19
Time Remaining: 26d 11h 29m
Buy It Now for only: $48.19

Other On30 Scale train items recently purchased through this site:

Hangman Creek Lumber Company DVD HO HOn3 S Sn3 O On3 On30 Narrow Gauge
O S Wiseman Models Metal Engine Kits Narrow Gauge
BTS 17143 On30 Laser Cut Narrow Gauge Cheat Run Trestle Craftsman Building
Ride the Sandy River Americas Largest Two foot Railroad Narrow Gauge
Cagneys Locomotive Works Miniature Railroad Supplier Narrow Gauge
Narrow Gauge Through the Bush Ontarios Toronto Grey Bruce and Nipissing
Varian 0572 K7360 306 Ionization Gauge I dont think its ever been used 
KATO N gauge 251 based super view Dancer appeared during coating 10 Car Set S
KATO N gauge E233 system 5000 series Keiyo Line through organized 6 both basic s
Kato N Gauge E231 System 0 Series Ch S bu Line 6 Both Basic Set 10 1520 M
KATO N gauge 251 based super view Dancer appeared during coating 10 Car Set S
Kato N Gauge E231 System 0 Series Ch S bu Line 4 Both hematopoiesis Set 1
KATO N gauge E233 system 5000 series Keiyo Line through organized 6 both basic s
KATO N gauge 209 based 500 series PS28 equipped Ch Sbu Line Basic 6 Car Set 1
Rare railway model HO gauge KATSUMI Moha 484 Kuha 481 form rail F S
Kato HO Gauge HV 21 HO Uni Track Automatic Traffic Signal S Set 3 131 Japan
Kato N Gauge Diesel Train 58 Based Non air Conditioned car Express Iide 7 Car S
N Gauge 10 1147 181 System 100 Fee Collectors Stand The Time Azusa Six car
Kato N Gauge Kashima Waterfront Railway 6006 Girl apos S Pan Danzer Speci