Personally I think all the later engine internals would be made in house by cosworth them selves and you would pay a premium for genuine parts even if you could get them which to be fare you never really see for sale.
Just build it to a good spec and you will be fine , if you've got a few grand to throw at it then buy a arrows crank , rods ,and some cp Pistons with some billet mains caps would make a super strong engine.
As for the head just a nice CNC head with oversized valves would be fine.
Turbo would cost a bit as it would need to have a Maram shaft for antilag .
Wastegate would cost a fortune so just use a tial etc.

Cheers paul