Remember that reverse gear usually uses 3 gears to do the job. The first gear is using just 2. The straight cut is due to the size of the gear cutter. A helical cut one would hit the reverse gear teeth if it was used. The factory used some other sort of cutter, I believe to be very expensive and hence not stocked by too many gearcutting companies.
Try these options:
G.T.O. ENGINEERING
Scarletts Farm
Scarletts Lane
Hare Hatch Nr Twyford
Berkshire
RG10 9XE
Tel: +44 (0)118 9401101
Fax: +44 (0)118 940 1372
Email:
gtoracing2001@hotmail.com