The Mach.2 is made by Sh. Engines and I'm 99% sure has a 10mm carb neck, using their "standard" small block carb, just anodized black.
just about any small block carb should work, you could try the one from a VX.18, though personally I like the Sh.18 rotary carb the most, they're hard to come by. I have a used engine sitting on the shelf that I could pull one from if you're interested in trying it.