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

Coca Cola Hawthorne Village Baggage Car
Coca Cola Hawthorne Village Baggage Car
$99.00
Time Remaining: 12d 5h 56m
Buy It Now for only: $99.00
On3 On30 WISEMAN SM 101 DRGW OPEN PLATFORM BAGGAGE PASSENGER CAR KIT
On3 On30 WISEMAN SM 101 DRGW OPEN PLATFORM BAGGAGE PASSENGER CAR KIT
$89.95
Time Remaining: 22d 11h 51m
Buy It Now for only: $89.95

Other On30 Scale train items recently purchased through this site:

Coca Cola Hawthorne Village Baggage Car
On3 On30 WISEMAN SM 101 DRGW OPEN PLATFORM BAGGAGE PASSENGER CAR KIT