I am sorry - i no longer sell these lenses.
You can use any old magnifying glass - but a fresnel will work MUCH better. You can get them in stationery shops - sometimes called 'page magnifiers' - or sometimes you see them sold in catalogues that sell things for older people.
Ebay should also stock them - don't pay more than 5 UK pounds for one - or 5 dollars in the USA. If you want to order a few try searching for wholesalers who will be able to get you them for around 1 pound each or less if you order 100 or more.