I haven't seen any foam air filter material 2 inches or greater out there. I initially had the same thoughts as you to use a thick piece of the foam air filter material but I eventually swapped out the oil bath component and inserted a WIX paper filter (part # 46192, ordered from Amazon $15) in the air filter bowl. Since the outer material of the air filter is metal, I fashioned a "seal" out of an old bicycle tube and slipped it over the top and bottom of the filter. When you tighten down the lid of the filter bowl it seals the upper and lower end of the filter and forces the air to be transferred through the material. It was an easy swap. There is a thread out there started by Kevin1957 that has some good info on converting from oil to paper air filter. Modify air breather oil to paper

1950 3100 5 Window
http://imgur.com/a/DAVYB