Try Brownell's
The typical reason for titanium parts in the firing mechanism is to reduce weight and therefore lock-time. If the firing pin is breaking "regularly" on his individual rifle, and this isn't a common, known problem in the design, then there's a very good chance that something serious is causing it, and the firearm isn't safe to shoot. Replacing the firing pin with one less prone to breakage because it's harder could cause a catastrophic failure, putting his safety in jeopardy.
Mark
Like what? Titanium pins are softer than the steel ones that Ruger uses. There's probably been a run of bad pins, and he says he doesn't want to go around the merry go round with Ruger anymore. The gunsmith who does the work will spot any potential problems.