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

Thomas Kinkade Lamplight Express Observation Car14 09004 004Hawthorne Village
Thomas Kinkade Lamplight Express Observation Car14 09004 004Hawthorne Village
$64.95
Time Remaining: 14d 21h 40m
Buy It Now for only: $64.95
ENHANCED BACHMANN On30 Painter of Light Observation Car
ENHANCED BACHMANN On30 Painter of Light Observation Car
$110.00
Time Remaining: 22d 49m
Buy It Now for only: $110.00

Other On30 Scale train items recently purchased through this site:

Thomas Kinkade Lamplight Express Observation Car14 09004 004Hawthorne Village
ENHANCED BACHMANN On30 Painter of Light Observation Car