Can anyone can recommend an online place to buy O rings for a gardena hose
system, please.

The official gardena are nearly three pounds for only 5 rings.

I have seen packets of 50 of the non branded ones for the same money on
line. They say they will fit both hozelok and gardena hose fittings. But i
have sometimes seen gardena rings listed as being 10cm whilst the hozelok
seem always listed as being 9 cm diameter.

Are the two systems using the same o-rings? Or are they slightly different
in size? I'm fed up with wasting water. Thanks.