S&W has phased out forged parts a long time ago. What they don't sell or use in-house they usually auction off to parts houses like Numrich. They no longer support older made guns with original replacement parts.
Luckily you can still find parts online, ebay, LGS, swap meets, shows, etc. and some are still as- new or unused. Just proceed cautiously when buying anything online of course.
There are also a couple of after market company's making some parts for discontinued revolvers, although I don't know anyone making Hammers and Triggers yet. If there become a large demand they just might one day. Unfortunately, the forging process seems to be waning in favor of casting which is cheaper and easier.
Sometimes S&W declines repair work on older guns because if they loose or break something they are not capable of repairing or replacing the part. They simply don't want the liability with no parts available to pick from.
When I owned and operated my Company we repaired anything with our name on it! If the exact march wasn't available we would repair or custom make a piece - but we were not huge like S&W is.