You can buy sheet styrene at most hobby shops (styrene is the plastic used for most plastic models), it comes in various shapes and sizes and is fairly easy to work with once you get used to it. Super glue works fine with both metal and styrene, or as mentioned 2 part epoxy (good if you need to fill gaps).
Two of the big companies for styrene
Evergreen
Plastruct
Many model and train stores also carry brass or aluminium shapes and tubing that might be helpful.
Also Roco mini-tanks might be helpful, its a smaller scale 1/89 (HO) vs 1/64 for hot wheels but some of the gun turrets etc might be useful. I can't find a website but they are pretty common at most hobby shops. Also 1/72 or 1/76 scale models of armored vehicles or aircraft might be handy and the scale is close enough for most purposes. Same goes for 20mm wargaming mini's.
There are several model building websites out there that are great for learning new tips or finding out where to get stuff.
Fine scale modeler (also a magazine)
http://www.finescale.com/fsm/community/forum/
Scale auto (also a magazine)
http://www.scaleautomag.com/sca/community/forum/
And I have a section on my own website where I show how to so some things (but no autodueling yet)
http://www.geocities.com/floydreinst...dels/Index.htm