Everything is available, but maybe not standard bits.

We had ours rebuilt last year with new forged rods and pistons, head polished and ported, crank knife edged, all new bearings gaskets etc for £4k.

That doesn't take into account otehr bits that youd probably want to replace during a new build such as oil pump (~£300) and water pump (~£400) etc

Gearbox was completely overhauled also with all new bearings and synchros at a cost of £660

New AP clutch will set you back around £400, a turbo rebuild around £350, some sort of tubular manifold (if you want to go that route) £300 - £900 depending on make

The list goes on....