Have you tried typing in Boost Mobile Samsung Galaxy S II case? You can also search for a Sprint case for the phone, since Boost Mobile is owned by Sprint, so it should be the same phone.

I am looking to buy a screen protector and case for my Boost Mobile Galaxy S II phone. I'm not sure if I can buy any case made for Galaxy S II phones, or if Boost Mobile's Galaxy has different dimensions to it and requires a differently sized phone case than the Galaxy S II phones from other brands.