I found some slide carbs for the SH12 for $29 new. They are a direct fit. Me thinks the only difference in the SH12 and SH18 is the bore and stroke. I think the carb is the exact same(venturi size that is). I will get out my SH18 slide and compare the openings with the SH12 rotary.
I went ahead and ordered 2 from Hobby People. Thanks guys for your help.
Now I just gotta find out what to do about the head. I may end up biting the bullet and buy that nova rc head.