Hi Erick
If you don't have any luck close to home finding " O " rings , try
www.ludowiciseals.com, they are in St Marys in Sydney. they supply all types of mechanical seals for engineering ( hydraulics, pneumatics etc. ) The size you want is 50mm ID x 1.85mm cross section ( 0.075" ).
Just measured my GSO finder, to be accurate, hopefully they will supply small quantities, you may have to buy in lots of 6 or 10, which I think would still be cheaper than buying a kit. I used to be an hydraulics maintenance fitter and have bought O rings from them before, though a few years ago now.
Regards
Jeff