I need my Shishkebab fixed and have no spare ones to do it myself. All the NPCs I've met so far don't fix any higher than 49%. Aren't there any better ones?

The best repair NPC in the vanilla game is Crazy Wolfgang, the caravan merchant. Once you invest in him his repair skill goes to 85%, IIRC. Of course, you have to keep him alive, which can be tricky in the mid to late game.

If you have the Point Lookout DLC, there's a glitch with Haley, the guy who runs the hardware store, that allows you to build him up to 100% repair. He never leaves the store, so keeping him alive is easy.

If you have the schematic for the Shiskebab, you could always scrounge up the parts and build a couple yourself to keep as repair items as well.

In the early game I sold a lot of Shishkebab parts, which are gone now, after a merchant reset. Aren't the parts finite? Do they respawn at merchants or even places?