Your best bet is finding someone with a core engine willing to part with the manifold. Otherwise, you're stuck buying it new along with the DISA valves.
I swapped it myself in under 2 hours. Pulling these things off is 10 times quicker and easier than the E36/E46. No more mess of wires and hoses underneath!
The wiring for the DISA valves is already on your current wiring harness too. The power gain is significant.