According to their web page Eastern Metal Supply (
www.easternmetal.com) makes 7" X 7" X 0.156" and 5" X 5" X 0.125" as stock items. The first problem is that both come in 24 foot lengths. The second problem is that their nearest location is in North Carolina.
Your best bet is to contact them and ask if they know of a distributor in your area who might have it in stock or know of a distributor who might be willing to cut and ship it.
Good luck. Getting this stuff quick isn't going to be easy.