eBay

This is a genuine SU manufactured (but Unipart packaged) carb damper for a huge range of SU carbs. The SU number is AUC 8102 and the Unipart number is GSU 320. THESE ARE NOW OVER £24.00 INCLUDING THE VAT FROM BURLEN, SO GET AS MANY AS YOU NEED HERE AT A BARGAN PRICE!!!
You can tell if it is the correct one for your carb by seeing if the cap/damper on you carb has "AUC 8102" written on it.
Amongst the cars it fits are:

Austin A110 Westminster
Austin Healey 100 BN2
Austin Healey 100S
Austin Healey 100-6 BN6
Austin Healey 3000 Mk1 BN6
Jaguar Mk VII
Jaguar XK 120
Jaguar XK 140
Jaguar Mk I
Jaguar Mk VIII
Jaguar 3.4 Litre XK 150
Jaguar Mk II (3.8 Litre, 3.4 Litre, 2.4 Litre)
Jaguar S-Type
Jaguar 240
Jaguar 340
Jaguar XJ6 Series I and II 1968 -1975
Rover 20
Rover 60 P4
Rover 75 P4
Rover 90
Rover 105
Rover 100
Rover 95

If you have any questions please ask.