The local hardware store will have all sorts of things you can use.
L-Brackets
Flashing (metal used in mounting gutters)
Theres allso a roll of aluminum stuff you can find in with the plumbing stuff that has holes in it every inch or so, this stuff is sturdy yet easily formed to shapes.
I would suggest goint to your local Home Depot, Lowes, etc and just look arround if you are in the right mindset you will start to see stuff that you can use for other applications of you arcade cabinet.
Hope it helps,
-Goz