i bought a sheet of 1/8" 7075 T6 from onlinemetals.com and was very happy with it. very good prices too. check this link.
http://www.onlinemetals.com/merchant...p=2&top_cat=60
you can specify the size too. i think a sheet of 1/8" 7075 that was 7" x 18" was only $35. or you can just buy pre-cut sizes.