Forgot to mention.
1/8" angle is easy to cut with a hack saw, but for those without industrial tools who do have to use 1/4" thick angle - I had, because 4" angle only comes in 1/4" thickness - there is this place in Seattle:
Online Metals. Once you know what size and length you want - and there is a good chance that you will need 4" or 6" long pieces - you check the box "custom cut". It costs very little, something like 50 cents per cut. Definitely worth paying to avoid pains of cutting 1/4" aluminum with a hacksaw.