I use the wire form political yard signs for my landing gear. It's similar to the the thick wire FT sells, 0.125" or 1/8 inch. It's hard to bend without a bench vice. If you don't have a vice, I'd go with the medium, 3mm.
Any suitable size wire will work, I've used the wire from a heavy duty coat hanger. Music wire is better, it's been hardened and has more springiness to it. Any decent hardware store and all big box building supply, like Lowes, will carry it.
