Might be worth checking good old ebay. Also worth considering an alternator from an aerlier 2.8 Fourtrack, think thay are very similar if not the same. Proberbly higher output also.
Search for a seller on ebay called "apodus", he has an ebay shop called "starter & alternator solutions", have used him a couple of times,bought a brand new starter for my F50 from him for around the £50 mark I think, worth a look!