If they were actually being refurbished on the IOW, then Bembridge outboards might be worth a call.
Other than that, I phoned a guy with an Ebay shop the other day who is stripping loads of old outboards at the moment, and only puts a small selection of parts in his listings. He was very helpful and would also be worth a call.
I found him by searching ebay for ‘Suzuki Powerhead’. Can’t access ebay at the moment to confirm his name, but he has a thick red band across his listings, and his phone number is listed if you click on ‘Contact details’ under the description.
RIBBED For extra pleasure.
Member of the ebay Blue RIB cover club.
Member of the Bombard 380 Aerotec club