ball faucet mixer tap in kitcken leaks

Hi All
I have a duetto and the tap in the kitchen is a single lever ball faucet tap. When switched on water leaks from the base of the tap. I have taken the tap apart and the problem appears to be two rubber rings which fit over the base of the copper inner of the tap and form a seal when the chrom  sleeve of the tap is slid down over the base. Does any body know where I can get replacements, or  could the fault be something else. Thanking you in advance for your help
best wishes
jataylor1
john

Have you tried asking Auto-Sleeper?