the only 22/45's that i absolutely know are drilled & tapped for a scope from the factory is the slab side 22/45 from davidson's.
they have an even longer barrel available in a 22/45 called a great 8 (an eight inch barrel, whil the other i mentioned has a 6-7/8 inch barrel), and i'm very sure ir has factory scope holes, but i haven't actully had one in my hand to see.