Found an advertisement in "Classic Motorcycle Mechanic":
NRP DIAPHRAGMS (in UK) sells replacement diaphragms for a range of motorcycles - specifically listing XV1000/TR1.
Tel./fax. 00 44 (0)161 832 8646 (I think one must call 00 44 161..... if calling from outside the UK). Mon-Fri 9:30 - 18:30; Sat 10 - 15.
Address: Unit 2, Station Approach, Victoria Station Concourse, Manchester, M3 1NY
..... since many have asked.
Happy motorcycling season!
Morten