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'.

HOn3 Silver Princess brass DRGW caboose in original box
HOn3 Silver Princess brass DRGW caboose in original box
$85.00
Time Remaining: 26d 32m
Buy It Now for only: $85.00
Bachmann On30 Scale Train Caboose Off Set Cupola Caboose White Pass Yukon 26564
Bachmann On30 Scale Train Caboose Off Set Cupola Caboose White Pass Yukon 26564
$54.19
Time Remaining: 29d 18h 23m
Buy It Now for only: $54.19
Bachmann On30 Scale Train Caboose Off Set Cupola Durango  Silverton 26565
Bachmann On30 Scale Train Caboose Off Set Cupola Durango Silverton 26565
$54.19
Time Remaining: 29d 18h 23m
Buy It Now for only: $54.19

Other On30 Scale train items recently purchased through this site:

HOn3 Silver Princess brass DRGW caboose in original box
Bachmann On30 Scale Train Caboose Off Set Cupola Durango Silverton 26565
Bachmann On30 Scale Train Caboose Off Set Cupola Caboose White Pass Yukon 26564