Mikey, just as easy and even cheaper to use are also copper strands - unravelled from standard, household electric cables. Actually, easier, since copper is softer - much easier to straighten (by rolling), and to cut - yet, at the lengths we're talking about (0.05"-0.10") remains plenty stiff enough for 500-scale landing gear (or gun barrels, etc.).

Typical landing gear specs for some Matty's Models aircraft can be found (halfway down) on my landing gear construction page. (Which also shows you how can also make everything - struts, wheels and all - using just plastic rod, and a thicker-type plastic glue.)

If going the wire route, and unsure of your diameter and/or you have to buy some new, the above diameters equate to roughly 12-14 "guage", at your local hardware store - ask or compare against that, and they will steer you right, buddy!

Cheers,

-Matty