1) If you have a cast manifold, you should be able to find someone local who can just cut it, and weld a flange to match your turbo.
2) Find a manifold designed for a turbo engine with the same cylinder head as your car.
3) Find a manifold for the conversion - Mitsi Elipse Turbos are a very common mod in teh USA - try EBay Usa.
What happened to the manifold that came with the kit???
For someone to make a good manifold from scratch, expect £700-£1000, I know Owen Developments charge £800 for the cast manifold which has been modified for the FQ400s....