As you may well know, Tony Iommi of Black Sabbath lost the tips of all his fretting hand fingers in a machine press just before the band started touring. He plays with lighter gauge strings and does have some sort of prosthetic tips, so they must be available, but I'm afraid I couldn't tell you where from. Maybe your doctor could advise?

I just did a google search on 'prosthetic fingertips' and Tony Iommi featured in all of the first 8 results!