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

On30 CRAFTSMAN MT BLUE SANDY RIVER  RANGLY LAKES LONG CABOOSE BODYINTERIOR KIT
On30 CRAFTSMAN MT BLUE SANDY RIVER RANGLY LAKES LONG CABOOSE BODYINTERIOR KIT
$69.95
Time Remaining: 7d 15h 47m
Buy It Now for only: $69.95
On3 AMB Accucraft DdRGW Short Caboose New lettering brake wheels  couplers
On3 AMB Accucraft DdRGW Short Caboose New lettering brake wheels couplers
$125.00
Time Remaining: 8d 14h 30m
Buy It Now for only: $125.00
AMS Accucraft AC83 131 RGS Brass Caboose NEW 1203
AMS Accucraft AC83 131 RGS Brass Caboose NEW 1203
$229.99
Time Remaining: 25d 11h 42m
Buy It Now for only: $229.99

Other On30 Scale train items recently purchased through this site:

On30 CRAFTSMAN MT BLUE SANDY RIVER RANGLY LAKES LONG CABOOSE BODYINTERIOR KIT
On3 AMB Accucraft DdRGW Short Caboose New lettering brake wheels couplers
AMS Accucraft AC83 131 RGS Brass Caboose NEW 1203