You can graft a Super hammer into a Blackhawk (either frame size), Vaquero or New Vaquero quite easily. Note that the mid-frame size Blackhawks are basically NewVaqs mechanically speaking but with improved sights.
You can also splice in a Bisley hammer but you have to modify the hammer some. It's not very difficult...basically the rear area of the hammer's "lower circle" area needs to be ground down to follow the profile of the stock (or SuperBlackhawk/Montado) hammer. Any decent grinding wheel will do
and it's not a high-tolerance area.
The sear fit IS critical and it's usually a drop-in. Be sure and do good basic tests to make sure it's OK post-swap - cock it, dry-fire it, cock it again and wiggle the hammer around to make sure it doesn't slip off the cocked position. Odds are you'll be fine.
Now there's one more thing to check: make sure the transfer bar isn't being "pinched". Flatgate and others believe transfer bar pinch is a factor in premature transfer bar breakage and I for one agree.
Step one: take the cylinder out, put the base pin back in so the action works.
Step two: cock it and dry-fire while holding back the trigger.
Step three: push forward on the hammer with some authority - not "crazy" but give it a shove.
Step four: while pushing forward on the hammer release the trigger.
If the trigger goes forward, you're fine. If it sticks back it is because the transfer bar is being "pinched" between hammer and firing pin and is holding the trigger back.
What you do next to fix it is annoying. Get some small files (PUT DOWN THE DREMEL, GRINDER OR ANY OTHER POWER TOOL!) and gently file on the face of the hammer that hits the transfer bar. Not the top-most area, the face of the "step" below that. This decreases the amount of "whack" being applied to the transfer bar, basically.
You need to test it for pinch a bunch of times as you file. I found it to be nearly a 2hr job on mine while watching TV - the hammer metal is hard as hell. I wrapped a small bit of rag around the base of the hammer as I filed with it cocked (but the gun mostly assembled 'cept for the cylinder) so I could test it between more filing sessions.
You want to stop filing JUST when the pinch ends. And then, if you filed with the gun assembled, you need to now take it completely apart and clear out the ground-up hammer metal before use.
I for one think this is vital if the gun is going to be pressed into defensive service, and useful on any other.
What else...ah. Yeah. There's one other source of hammers - Ron Powers at Power Custom. He can sell you a matched hammer/trigger setup that is a lot like dropping in a high-dollar action job yourself. He sells hammers in regular and Bisley flavors with the Bisley set up to fit in non-Bisley grip frames already.
There's a rumor he also sells some in SBH shape as well...you'd have to call and ask.
The prices are high - $180 or so for the hammer/trigger set. But it may be worth it to you - a gunsmith would charge $125 for the same work level, plus shipping, so the cost is about a wash and you don't have to ship your gun anywhere. Plus it's a drop-in Bisley solution for non-Bisley grip frames.