Informative link:
Everything you ever wanted to know about tinfoil.
I'm afraid I no longer sell tinfoil. It was always just a sideline I did as a service, not a profit-making venture. The problem is that the cost of foil kept going up along with other metals, reaching astronomical levels. I've dealt with two suppliers, leaving the first because the second beat them on price and was also willing to accommodate running a special order at 1.5 mils rather than 2.0 mils which is a standard. Back in 1878 the 2 mil thickness was favored early in Edison's experiments, but by the time the phonograph was on the exhibition circuit it was found that 1.5 offered the ideal balance between ease of use and high quality recording.
Anyway, supplier number 2 went into the stratosphere so I returned to the first supplier and accepted 2.0. But they kept going up as well.
I had to buy 10 rolls at a time (1 pound each) and I was selling at most 3 or 4 a year. The economics of that proposition soon made me realize that although I really liked to be able to keep collectors supplied, it simply wasn't viable anymore.
I hope maybe that will change in the future. There has been some pullback in commodities pricing so it may once again become viable.
One suggestion I can offer is to ask your dentist. Once upon a time tinfoil was used in dentistry, and some (not many!) dental supply wholesalers still have stocks on hand. Dental foil is made in 1.0, 2.0, and 3.0 mils. The first makes great recordings (easily indented) but is very hard to work with because it's so flimsy. It's just to thin and easy to crease/tear. 3.0 is much too thick and doesn't work well at all. So if you're lucky, maybe you can get a pound or two of 2.0 through your dentist, or if his local supplier is amenable, directly from them. Or if you're really lucky, maybe your dentist has some left over and would be glad to be rid of it. I think it has been completely supplanted in modern dentistry. I know my dentist hasn't used it in 20 years.
I did a ton of research on foil production about 15 years ago when I took on a project to supply the Ford Museum. There just aren't many companies in the world who make it anymore. The sheets I had custom-produced for the Ford, and also for collectors, were made in Germany. The minimum order was 500 pounds! The irony is that when the crate was delivered to my door, it was only about a 2-foot cube. Tiny. But completely impossible to remove from the truck because of the staggering weight; the poor driver thought he was delivering to a warehouse with a forklift, not a home garage! I had to open the crate in the truck and remove each paper-wrapped bundle individually. Foil is heavy.
Aluminum foil will work in a pinch. It is a very hard material as compared to real tin so it has a lot of surface noise. That can be minimized somewhat by wiping a thin layer of oil over the surface just before recording and playback. That bit of lubrication really helps, but it's still more noisy than real tin. On the other hand, aluminum can give slightly louder recordings, and they hold up for more playbacks. It does take a bit more care in getting the adjustments exactly right since it tears more easily than tin but it is the alternative used by most people today.