There is a guy on eBay selling replacement filters for these air cleaners. But just like the old ones these can be somewhat flammable (just as some of the old fellers that melted theirs). When I bought my replacment I talked with the gentleman and he said he was working on getting non-flammable material.
Keep in mind he has a 1/2 thick and 1/4" thick version depending on the manufacture of the air cleaner. Below is a link (click on it) to one of his auctions.
Round Fly-Eye Air Cleaner Filter