I have noticed that Grocery stores & drug stores like Walgreens stock Matchbox singles. I know that Safeways out here have a couple of racks of them. My 2 year old son knows it too & always wants to get them whenever we go grocery shopping.
Thanks for that. We've got some Walgreens around here but I'm rarely in them I'll have to check again.
I was at another Dollar store yesterday didn't find any 10mm compatible tanks, but there was a "Police boat" (apparently a repainted "Bay Brigade" fire boat) that might have potential for 10 or 6 mm.
Not sure why I didn't buy this one.
Also, My son picked out the "Heavy Railer"
At first I wasn't impressed with this engine that doesn't run on any known rails and has no other cars available, but it has a futuristic look and the detailing (notice the tinystairs in front) does seem well suited to be the engine for a 6 or 10mm super train?
I've found the matchbox wiki pretty useful.
http://matchbox.wikia.com