You might pay a visit to your local fishing tackle shop. I dealt with this problem (small diameter, fat filters) by buying a case used for fishing flies. It is made out of closed cell foam with a fabric covering. I did some -- uh -- "creative" work on it with a temperature controlled soldering iron. I then cut some craft foam and glued it in with rubber cement to create pockets for the filters.
It hasn't seen much use yet, but so far, so good. I have some doubts about the concept of magnetic catches, but they seem to work. Larger sizes are available, but this seemed about right for me. Here in the US, LL Bean carries them, I think it was about $10.