Big Mulies are hard to find everywhere. Increased hunting pressure, increased poaching, mismanagement of hunting regs by local Game & Fish authorities. . . all have a detrimental effect on trophy Mulies. Or anything else.
I live in Cheyoming and have personally seena lot of20+ inch mulies.
Why do you have to use an outfitter? If you do, I recommend looking for an outfitter that offers "assisted" hunts instead of fully guided. I think they are more fun, and have to be less expensive.
I would have to recommend Colorado just because I think it is easiest to get a license there. But I see a lot of hunting shows bringing down big Mulies in Canada as well.