NM Super hammers are easier & cheaper to find. The OM's do cost more & aren't readily available. If you are looking for NM hammer, Brownell's, Midway, Numrich Gun parts, Jack First Gun Shop, all are good places to start as well as placing WTB ads around here.
For OM Super hammers, Numrich, Jack First, gun shows, ads here, etc all can be places to find such stuff. I know I buy all such parts when I find them at reasonable prices, as they don't make OM hammers anymore.