Above suggestions are all spot on. I would suggest staying away from brass framed guns as was said before. Pietta and Uberti are both fine. As much as I like ROAs, you can find something cheaper and just as reliable. I like SS guns. Some people don't. I also like blued guns, just prefer SS. An 1860 or an 1858 would be my preference. Good starting points. The Walkers, Dragoons etc etc are nice also, and many people start with the 1851. Personally, '58 or '60 would be my bet.
You will need a powder measure, nipple wrench, balls, caps, powder, cleaning kit and perhaps over powder wads. Also lube (crisco is fine). I suggest you read the sticky 'so you want a cap and ball revolver' found at the beginning of the Blackpowder Forum.
I got my dad into BP a year or two ago. I sold him (yes sold, he aint the type to take free stuff, and yeah I lost money on the deal
) an 1851 Pietta. He has 8 years in the armed forces and is in his 60s, been a gun owner since the 1950s. He had never shot a black powder gun before this one. He still likes modern stuff, but the BP is growing on him. I think you're idea is great. Get your dad one. Makes for fun times.