If anyone is looking for the wire used in the Scout and Sportster or similar FT builds then this steel rod and these wheels were a perfect match, the wire is a 500mm length, you will have a little bit left left over. I had to ream the wheel holes out a little bit to 3.2mm.
3mm dia is their minimum diameter, which looks a bit thick (heavy) to me. Also, it's EN1A, which is plain ordinary low carbon mild steel. We normally use steel with a higher carbon content to be springy. I'd say that the best place to get it is most likely your local model shop, where it comes in 3ft lengths for less than £1 each. It used to be called "piano wire", but I don’t hear that name much these days. I sometimes see "music wire" or "spring wire".
I haven't measured it, but I'd say that 2mm would be about right, which is 14g.
Nearest model shop to me is an hour away. It doesn’t sell any aircraft parts or tube stock.
Will look into slightly higher carbon steels. I picked 3mm because the wheel centres were that size if you wanted larger than 50mm wheels.
FT gear wire in their store is 3.2mm thick. Even the medium wire is 2.6mm 3mm Piano wire and 2.5mm wire links from EBay. I see the other lengths are K&S metals which in my part of the world are easiest to get from Cornwall Model Boats.
I have found some wire yard signs make excellent landing gear. If you are lucky enough to have a farm supply store near by, high tensile fencing wire also works. Of course, the old standby, good thick wire from a clothing hanger.