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: 17d 14h 54m
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: 24d 18h 3m
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