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

HAWTHORNE VILLAGE BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
HAWTHORNE VILLAGE BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
$27.97
Time Remaining: 5d 21h 31m
Buy It Now for only: $38.00
H O Scale Hawthorne Village Coke Coco Cola Santa Train Freight Box Car
H O Scale Hawthorne Village Coke Coco Cola Santa Train Freight Box Car
$49.99
Time Remaining: 6d 2h 17m
Buy It Now for only: $49.99
On30On3 Narrow Gauge Custom Scratch Built On30 Boxcar and Caboose Nice Details
On30On3 Narrow Gauge Custom Scratch Built On30 Boxcar and Caboose Nice Details
$185.00
Time Remaining: 7d 7h 17m
Buy It Now for only: $185.00
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 15 nd
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 15 nd
$71.66
Time Remaining: 9d 14h 30m
Buy It Now for only: $71.66
ON3 ON30 SILVER CITY MODELS DRGW 1872 12 4 WHEEL BOX CAR KIT
ON3 ON30 SILVER CITY MODELS DRGW 1872 12 4 WHEEL BOX CAR KIT
$36.00
Time Remaining: 10d 2h 23m
Buy It Now for only: $36.00
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 315 nd
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 315 nd
$71.66
Time Remaining: 10d 14h 36m
Buy It Now for only: $71.66
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR J E B STUART BOX CAR 005
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR J E B STUART BOX CAR 005
$59.99
Time Remaining: 11d 6h 22m
Buy It Now for only: $59.99
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 605
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 605
$71.66
Time Remaining: 16d 17h 47m
Buy It Now for only: $71.66
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 606
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 606
$71.66
Time Remaining: 20d 18h 51m
Buy It Now for only: $71.66
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 603
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 603
$71.66
Time Remaining: 22d 22h 53m
Buy It Now for only: $71.66
HOn3 Wooden Boxcar Built
HOn3 Wooden Boxcar Built
$29.99
Time Remaining: 23d 10h 55m
Buy It Now for only: $29.99
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 3145 n
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 3145 n
$71.61
Time Remaining: 23d 14h 10m
Buy It Now for only: $71.61
Bachmann On30 Scale Train 18 Box Car W Murphy Roof Gray 2 box 26553
Bachmann On30 Scale Train 18 Box Car W Murphy Roof Gray 2 box 26553
$73.15
Time Remaining: 25d 23h 12m
Buy It Now for only: $73.15

Other On30 Scale train items recently purchased through this site:

ON3 ON30 SILVER CITY MODELS DRGW 1872 12 4 WHEEL BOX CAR KIT
HOn3 Wooden Boxcar Built
HAWTHORNE VILLAGE BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
H O Scale Hawthorne Village Coke Coco Cola Santa Train Freight Box Car
Bachmann On30 Scale Train 18 Box Car W Murphy Roof Gray 2 box 26553
On30On3 Narrow Gauge Custom Scratch Built On30 Boxcar and Caboose Nice Details
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR J E B STUART BOX CAR 005
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 3145 n
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 605
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 15 nd
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 315 nd
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 606
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 603