You should be able to buy original Zeiss Ikon-branded filters for a reasonable amount. I think that I paid on average about $5 for each of my filters: Dark red, orange, green and yellow.

I also found a nice push-on lens shade that came with a bunch of other things.

The later Ikonta cameras used filters that screwed onto the outside of the lens: 35.5mm filters for 6x4.5 and 6x6 and 40.5mm for 6x9.

These filter sizes were also used by other Zeiss Ikon cameras (Ikoflex, Tenax II, Contax, etc.).

Enjoy that camera. I've made some great images with Tessar-equipped Ikontas and Super Ikontas.