Hi Doc,
Let's set calibre aside and address easy to fix or get parts aspect of your inquiry.
If one insists on a double action revolver, Rugers are absolutely the most reliable revolver. Granted they lack the selection or finish of S&W or the trigger pull of the Colt Python, but neither of these makes compare with Ruger for absorbing abuse and neglect. Kodiak already mentioned about the Ruger he qualified with.
From a maintenence perspective, (disassembly for servicing, cleaning, etc.), they're all about on par. Note, I'm not talking about replacing parts, just complete disassembly and cleaning.
Regarding repairing or tuning, Ruger and S&W are about on par but S&W will yield a superior trigger pull. However, Rugers revolvers subject to the same use and abuse as Colt or S&W will require less maintenance than either.
Colt Pythons require extensive training and practice to repair or tune and I can't recommend it to novices. Unlike newer Colt revolvers, Pythons are truly Old World Guns requiring Old World Craftsmen. It is very much like the British Webley inside.
On the newer Colt revolvers, the internal mechanism functions very much like the S&W and if you understand how a S&W works, you can figure out the newer Colts (so they're easy to work on).
Parts acquisition for S&W revolvers is probably easier than Ruger or Colt. But replacement of parts for revolvers are few and far between.
I've been trained to work on all three makes and own all three brands. While I love my Python and Diamondback 22 for sheer shooting joy and my M29 for wandering about in the woods (cat country), if I had to rely on any revolver, it would be the humble Ruger.
Turning to semiautomatics and using only the criteria of easy to fix or get parts, there's only two types I can recommend:
Glock - With about four hours of training, all you really need is a pin punch to work on a Glock. They're that simple.
The only other gun which isn't hard to work on is the M1911. Olympic Shooter and former Gunsmith Bob Chow was one of the first to point it out. With a little bit of training, it wouldn't take much for you to be able to swap parts. Unlike the Glock though, understanding the intracies of the Browning's 1911 design, how parts interact with one another, proper sear/hammer relationship, adjusting extractors, installing safeties, fitting barrel bushings, etc. is another matter and you should spend at least a week (40 plus hours) studying and assembling one. Enrolling yourself in a NRA gunsmithing course is about the easiest and least expensive way to acquire this knowledge and develop your skill.
One definite advantage of the 1911 is the availability of parts. Glock parts are easy to get, but 1911 even easier.
To summarize, if you have to get a revolver, go Ruger. If you go semiauto, go Glock or 1911.
Myself, I like the P220 in 45 but my selection process is different.
