Just a few ideas:
http://www.amazon.co.uk/s/?ie=UTF8&keywords=die+cast+buses&tag=googhydr-21&index=toys&hvadid=7066145360&hvpos=1t1&hvexid=&hvnetw=g&hvrand=21059897111203109688&hvpone=&hvptwo=&hvqmt=e&ref=pd_sl_822l9oy8o5_e but do a search on Amazon.com for die-cast buses
eBay through VigLink (I know you don't like it but) should have collectibles for collectors - bus tickets, bus timetables etc
Use the search term: 'diecast buses affiliate'. I found:
BBC shop is covered by Viglink.
What about writing about great bus journeys and link to travel sites that offer the trip.
When you say buses do you also include coaches? Coach tours (again through Viglink affiliations) could be offered on your articles.
Basically anything can be monetized if you think laterally and hard enough (and use the monetizing options at Wizzley, or join the affiliate programs that offer products that relate to the subject you are interested in writing about in some way.