Tire size question on 10.5 Wheels

[chalosf]

I found a great price on wheels but need tires..I will be putting 275/35/18 on the front for the 9" wheels but for the back I have 10.5" wheels and was wondering if they make 305/35/18 or 315/35/18 tires and will they fit? my 01 gt

 

[SonicStangGT]

I have 315/35/17 MT Drag radial on my 04 with it lowered and it does not hit, but its close. Not sure how a 18 would do, I think it should fit as I have room for a bigger wheel or tire.