I only know Kodak Thin & Lite Lenses. They are thinner than the lenses made by other kind of materials of the same degrees. You can buy them from approved Kodak Lens stockists or from the expert independent opticians at your local Kodak Lens Vision Centre. Hope this helped!
Once I came across the thinnest lenses in "My Eyewear 2go". You can buy high index glasses online from this online store. There are 1.67 Index, 1.70 Index, 1.74 Index, 1.80 Index, and 1.90 Index. The 1.90 Index is the thinnest lenses. I think the price may vary from different index, so you'd better choose the one that is fit for your degrees other than buy the thinnest lenses.
I suggest you to have a look in the nearby eyeglasses stores. Some stores will not sell this kind of lenses while other stores may sell. I have asked all the stores around my school but I haven't found a store that sold the thinnest lenses. The boss told me that the thinnest lenses were more expensive, and customers of high degrees would choose another kind of lenses (thick lenses but less weight), so they would not get that kind of lenses from the wholesaler. But you can have a look in big eyeglasses stores. Maybe they can provide you with the thinnest lenses. Good luck!
The glasses with the thinnest lenses possible for high prescriptions are likely going to be high index 1.90 glass lenses glasses. 1.90 is the highest index lens material available on the market today, and it comes in glass, not plastic. Since high index glass lenses are somewhat heavy, you should order them in a frame that fits you very well. They are also highly scratch-resistant and durable.