Polarizer for circular fishey?

I have the sigma 8mm f/4 fisheye and it says it comes with a gelatin filter holder in the rear. Where do i find these filters? I used ebay real quick for gelatin filters but come up with these huge kodak filters.

can someone help me out?

What you'll have to do is cut the gel filter to fit the holder. There's no polarizing gel filter that I've ever seen, and on a fisheye, the effect would look uneven in sky photos. What you can do though is get a Neutral Density gel filter (2x-4x), which will give you some polarizing effect without the unevenness.

Thanks. I eventually figured it out. I went out and got my lens while it was 22*outside and started looking around the instructions. Now i just need to pickup some film.

You'd also find the necessary rotation of the polarizer in a rear-mount gel filterholder to be extremely difficult as it's only accessable when the lens is off the camera.