Z1OwnersClub GB

Here's a list of bikes that I found that have 20mm dia rear wheel spindles.

So no messing with the bearings to get them to fit...just need to sort the correct spacers.
Not definitive...and a bit questionable about the dates...and I have no idea why left & right are there..but a good starting point.

20mm
H**** CR250 M 73-76 (Left)
CR250 R 78-80 (Right)
CR250 R 81 (Left)
MT250 74-76 (Left)
XL250 72-76 (Left)
CB360 74-7 (Left)
CB400 75-81 (Left)
CM400 E/A/B 79-81 (Left)
CB450 65-74 (Right)
CB450 Tc 82 (Left)
CM450 A/C/E 82-84 (Left)
CR450 81 (Right)
CR450 R 82 (Right)
CB500 71-76 (Right)
CB550 F 75-77 (Right)
CB550 K ALL (Right)
CB650 C 79-82
CB750 A 76-78
CB750 C Custom 80-82
CB750 F 75-78
CB750 F/K/L 79-82
CB750 K 69-78
CB750 SC 80-83
VF750 C/C2 94-98 (Left)
VF750 D 94-97 (Left)
VF750 F 83-85
VRF750 F (Left)
PC800 89-90 (Left)
CB900 C 80-82 (Left)
CB900 F 81-82
CB1000 C 83 (Left)
CBR1000 F 87-88 (Right)
CBR1000 F 90-91 & 93-96
GL1000 L 75-79 (Left)
VF1000 F 84-85 (Right)
CBX1050 79-82
CB1100 F 83
CBR1100 XX 97 (Left)
GL1100 A/I 80-83 (Left)
VF1100 C 83-86 (Right)
VF1100 S 84-85 (Right)
Kawasaki GL1200 A/I/L/SE 84-87 (Left)
KZ750 B1/B2 76-77
KZ750 B3/B4 78-79
KZ750 G 80
ZX750 89-90
KZ900 76-77
ZL900 A1/A2 85-86
Z1 900 73-75
KZ1000 A/B/G 77-80
KZ1000 C 78-81
KZ1000 E 79-80
KZ1000 J1-J3
KZ1000 K 81-82
KZ1000 M1 81
KZ1000 P 82-97
KZ1000 R 83
KZ1000 D Z1/R 78 & 80
ZG1000 86-93
ZG1000 94-97
ZL1000 A1 87
ZX1000 A 86-87
ZX1000 B 88-89
KZ1100 A1-A3
KZ1100 B1/B2 81-82
KZ1100 L1/R1 83
KZ1100 R1 84
ZN1100 B1/B2 84-85
ZR1100 A1-A5 92-95
ZX1100 A1/A2 83-84
ZX1100 E1-E3 95-97
ZX1100 C 90-92
ZX1100 D 93-97
ZG1200 86-97
KZ1300 79-82
ZN1300 83-88
VN1500 87-97
VN1500 D 96-97
VN1500 B 87-90
Suzuki TM250 72-75 (Left)
TS250 71-81 (Left)
TM400 71-75 (Left)
TS400 72-77 (Left)
RE5 75-76 (Right)
GT750 73-77 (Right)
GV1400 86-88 (Right)
Yamaha XS360 76-77 (Left)
RD400 76-79 (Left)
XS400 77-81 (Left)
XS400 S 80-82 (Left)
XS500 76-78 (Right)
TX650 74 (Right)
XS750 77-79 (Right)
XS850 80-81 (Right)
FZR1000 89-93 & 94-95
GTS1000 93-94
FJ1100 84-85
XJ1100 82-83 (Right)
XS1100 78-79 (Right)
XS1100 G/H 80-81 (Right)
XS1100 79-91 (Right)
FJ1200 86-93
VMX12 85-97 (Right)
XVZ12 83-85 (Right)
XVZ13 86-93 (Right)
XVZ13 (Right)
H**** CR250 M 73-76 (Right)
CR250 R 78-80 & 87 (Left)
CR250 R 81-82 (Right)
CR250 88-89 (Left)
MT250 74-76 (Right)
XL250 72-76 (Right)
XL250 R 82-83 (Left)
XR250 R 86-95 (Left)
CR450 81 (Left)
CR480 R 82 (Left)
CR500 R 87-89 (Left)
FT500 82 (Left)
XL500 R 82 (Left)
CBR600 F 91-96
CBR600 96
XL600 R 83-87 (Left)
XR600 R 85-97 (Left)
CB750 SC 84-85
VF750 C 85-88
VF750 C/C2/D 94-97 (Right)
VF750 C/C2 98 (Right)
VFR750 86 (Right)
VT750 C 86
PC800 89-90 (Right)
VT800 88
CB900 C 80-82 (Right)
CBR900 RR 93-97
CB1000 C 83 (Right)
CBR1000 F 87-88 (Left)
GL1000 L 75-79 (Right)
VF1000 F 84-85 (Left)
VF1000 R 84-85 (Left)
CBR1100 XX 97 (Right)
GL1100 A/I 80-83 (Right)
ST1100 A 91-96 (Left)
VF1100 C 83-86 (Left)
VF1100 S 84-85 (Left)
VT1100 C 85-96
VT1100 C2 95-97 (Right)
GL1200 A/I/L/SE 84-87 (Right)
GL1500 (Goldwing) 88-97 (Left)
GL1500 (Valkyrie) 96-97 (Left)
Kawasaki KDX/KX420 80-81 (Left)
ZX600 E 93-98
ZX600 F 95-97
KL650 87-97 (Right)
ZX750 H1/H2 87-90
Suzuki RM250 87 & 90-91
RM250 88-89 (Right)
RMX250 89-96 (Right)
DR350 90-97 (Left)
DR350 S 90-96
RE5 75-76 (Left)
GSF600 96-97
RF600 R 93-95
DR650 SE 96-97
XN85 83
GS750 B/C/EC/N/EN 77-79
GS750 LN/LT/LX 79-81
GS750 ET/EX/EZ 80-82
GS750 TZ/TD 82-83
GSX750 SZ 82
GS750 SD 83
GSX-R750 88-92
GT750 73-77 (Left)
RF900 R 94-97
GS1000 C/EC/N/EN/ET/ST 78-80
GS1000 LN/LT 79
GS1100 E/ES 80-83
GS1100 SZ/SD 82-83
GS1100 G/GK/GL 82-84
GSX1100 F 88-93
GSX1100 G 91-93
GSX-R1100 88-92
GSX-R1100 W 93-97
GS1150 84-86
GSF1200 S 96-97
Yamaha YZF600 RG 95
YZF600 96-98
XS750 77-79 (Left)
H**** CR250 R 82 (Left)
CR250 R 83-86
CR250 R 87 (Right)
CR250 88-89 (Right)
CR250 90-97
CR480 R 83
CR500 R 84-86 & 90-97
CR500 R 87-89 (Right)
Kawasaki KDX250 D 91-94
KL250 82-84 (Left)
KLX250 R 94-96
KX250 85 (Left)
KX250 86-97
KLX300 97
KX500 B1 85 (Left)
KX500 86-93
KX500 E6 94-96
KX500 E9 97
KLX650 C1-C4 93-96 (Right)
KLX650 A1-A3 93-96
SUZUKI RM250 88-89 (Left)
RM250 92-97
RMX250 89-96 (Left)
DR350 90-97 (Right)
DR350 S 97
GSX-R750 85-86
GSX-R750 87
GSX-R1100 86-87
YAMAHA IT250 82-83
WR250 Z 91-98
YZ250 81-98
YZ250 WR 89-90
TT350 85
IT465 81-82
YZ465 80-81
IT490 83-84
YZ490 82-90
TT600 83-86
Kawasaki KLX650 C1-C4 93-96 (Left)

My local bearing stockist makes lists like that too. And youre right it is not exhaustive. I saw some really nice ZZR wheels on ebay but in the end decided to go for the wheel which was to hand and just ordered bearings with a 20mm internal where the standard was 17mm. No cost implication.
I think left and right refers to the sleeve on the spindle which normally carries the sprocket hub so is therefore increased in size the normal wheel bearings in that wheel probably having a 17mm internal.

AL