You might be able to buy a wig and push it back on the scalp and create the front of the hairline yourself. Human hair wigs look the best.
What material is you Nicholson head? If it's soft (silcone, latex/polyfoam,etc) you could punch the hair in - or - if it's a plaster or resin type of material you could try laying the hair. You'd have to research laying hair, it's a makeup effects technique. Takes a lot of practice though. Punching too, for that matter.
The last suggestion would be to buy a lace front wig. It's not a whole wig, only the front portion. Lace looks a lot more natural than your normal thick foundation wigs. You could then cut up the lace front to create the receding hairline. It would still be tricky.
But really, the only way to have a quality hair piece is to have it custom made...but they are really expensive.
Not sure if I helped, but there's some info you may or may not have been aware of already. Good luck.