What Size Gasket Do I Use

I have a 305 thats been stroked to a 334......... the cylinder bore is

3.766(a .030 overbore) originaly 3.736........ what size gasket should i use....... ive read alot of stuff about the size and thickness but what size should i use and if i have to special order one, where can i buy it...... how big of a diameter should the gasket bore be?.... the same size as the cylinder bore or slightly bigger????? HELP PLEASE