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

HOn3 Brass PSC Mack Railbus Type AB plus Vintage Vehicles Kit
HOn3 Brass PSC Mack Railbus Type AB plus Vintage Vehicles Kit
$149.16
Time Remaining: 1d 19h 14m
Backwoods Miniatures Mack AC Railbus brass kit powered Sn3
Backwoods Miniatures Mack AC Railbus brass kit powered Sn3
$305.09 (3 Bids)
Time Remaining: 1d 22h 44m
Bemo HOm HOe DR VT 133525 Wismarer Rail Bus TSL
Bemo HOm HOe DR VT 133525 Wismarer Rail Bus TSL
$299.99
Time Remaining: 27d 10h 33m
Buy It Now for only: $299.99

Other On30 Scale train items recently purchased through this site:

Backwoods Miniatures Mack AC Railbus brass kit powered Sn3
Bemo HOm HOe DR VT 133525 Wismarer Rail Bus TSL
HOn3 Brass PSC Mack Railbus Type AB plus Vintage Vehicles Kit