Try volksmagic or Kingfisher Kustoms, both in Olbury / Smethwick west mids they both deal in second hand if that's what you are after.
VW Heritage also do them, or maybe this will fit ? http://www.ebay.co.uk/itm/VW-CAMPER-STARTER-MOTOR-12V-GEN-VW-inc-VWB-A-C-W-C-/230727720108?pt=UK_Campervan_Caravan_Accessories&hash=item35b8719cac#ht_500wt_1413
take your old to starter motor repairs shop.....was one in london postcode e2 that does mail order repairs ...ill drop by to get his card and post you his details if you want