Yes Atlas made the caboose in O scale and O Gauge several years back. Here is a photo of my long British Columbia Railway train running with the caboose. https://ogrforum.ogaugerr.com/...2#103777491008846452
Central Hobbies https://www.central-hobbies.com/ in Vancouver B.C. still has Atlas British Columbia Railway RS3's in stock in O gauge. A bit more detailed then the Railking MTH version you have. They still may have some other BCR freight cars in stock. Can also check with Kelly's Kaboose in Savona. https://kellyskaboose.ca/
Both of the above store's carry the Canadian Toy Train association custom runs of engines and freight cars. The club has done many items in BCR and PGE Pacific Great Eastern (the name of the company before it was renamed to BCR) Here is a page of our clubs special runs; https://www.canadiantoytrains.org/canada-club-cars/ The red white and blue BC Rail caboose is near the bottom of the page. You can also contact the club to put a wanted link on the club website or they can e-mail to the club next newsletter saying you are looking for the Green Atlas British Columbia Caboose. Atlas, Weaver and MTH also released many other freight cars in the green. If you are in US and buying from Canada remember that the US $ is high to the Cdn $ so anything you buy will be considerable less with the exchange rate.