If you have buy new, then the cheapest will probably do, Varga are about £80.00 on the Bay. Get the 37mm lens holder. Secondhand can sometimes be found on the Stirton forum but they tend to be the more expensive models anyway and might end up costing you more than a new Varga pair.

Varga accessories are available from Intershoot but I wouldn’t be in too much of a hurry to get an iris, get a properly prescribed lens sorted out first. Ask around in your club, because people must use opticians for similar purposes. There are quite a few shooting knowledgeable opticians around the country. Once again, Stirton is a good place to ask that question.

I don’t know how old you are, but very many years ago I was told that if you are over 40 and not wearing glasses to shoot, then you probably should be. In the light of experience I would agree with that👓

Rutty