I recently picked up a couple of spare bolts from a guy on abusedguns.
Colin Green had some stuff a while ago but not anymore.
I have bought a 1903a3 rear sight complete and other odds and ends from Numrich in the past.
There was no problems doing this.

You certainly did pay a pretty penny for it.....but in saying that it's a fine looking rifle.
I picked up my 1903 Mk1 for $500 from a guy in Proserpine {NQ} not so long ago.

You can get away with using Swede stripper clips, they work fine.
One thing for sure is that you'll enjoy shooting it..and you'll be amazed at how well they shoot.