For those of you interested in cowboy action shooting, first find the SASS-affiliated clubs in your area here:
http://www.sassnet.com/clubs/
Step two: Whether you are mildly curious about the game are dead-set or you are absolutely certain this is the game for you, I'd recommend that you resist the understandable temptation to buy guns, leather and other gear before you have attended a couple of local matches. Too often I have seen new shooters show up after spending serious coin on equipment, only to find out that what they bought the wrong stuff. Cowboy shooters are usually happy to let "prospects" handle their equipment. At many of our local matches there are folks with good used leather and firearms for sale, too.
On the other hand, if you already have something that would be legal for use in the sport, by all means bring it with you. Some clubs offer "new shooter clinics" or "practice days" to let new folks learn the ropes outside of the pressure of a match.
To answer a couple of specific questions in this thread: Yes, Ruger Blackhawks and other adjustable sight-equipped SA revolvers are legal for most categories, assuming they are between .32 and .45 caliber. Ruger has produced lots of Blackhawks so there are lots of good used ones out there.
Can you use one revolver, and reload it on the clock? YES. Since virtually all of our stages call for ten pistol rounds (we load the wheelguns with five rounds with an empty chamber under the hammer), if you have only one revolver there are two options under the rules. You can either fire five rounds, then reload five more "on the clock", or you can fire five rounds and take the penalties for the unfired pistol rounds.
As a practical matter, here's what happens when a new shooter with a single revolver shows up for a match: Another cowboy (or cowgirl) will offer the loan of a second revolver each time the new shooter goes to the loading table!
Every cowboy shooting club I know of wants new shooters and will do what they can to help new folks get started. My local club offers two "multi-gun" matches: cowboy action and modern Three Gun. The Three Gun matches are so popular that the matches fill up every time, and they have to turn shooters away. We've never had to turn people away who want to shoot cowboy.