Best place to get parts?

hipshot for the bridge and tuners

pickups you have anywhere from lindy fralin to seymour duncan

pickguard you can get straight from Fender, as with everything else on your list.

 

I'm ordering a few things from Hipshot... http://www.hipshotproducts.com/

I've heard good things from them... I'll tell you how it goes...

As for pickups, http://www.bestbassgear.com/bass-pickups.htm is a pretty reliable place to go... They also sell Badass bridges there...

 

www.warmoth.com has bridges and tuning keys.

There's some company called Jeannie's (or something like that) that supposedly does custom pickguards, although I've never dealt with them. I'm sure they could whip up a standard P-Bass guard with zero effort.