Valve Stem Oil Seals

I am currently rebuilding a 8:1 head for my Series 2a petrol, unfortunately after purchasing a brand new set of NOS valve stem seals, I find that I have misplaced them (read lost or thrown out with the rubbish). Can anyone indicate which are the best alternative seals to the originals? I ask because there does appear to be a lot of disgruntled owners out there who have done similar rebuilds with aftermarket stem seals only to find that the seals either fail or ride up the stem after a very short time, thus requiring a further strip down. Better still has anyone out there got a full set of NOS seals that they no longer require?
All answers and offers greatly appreciated.

try etc4709g and etc4751g

Thank you.