I have a set of EOS clip in filters for sale. They are only compatible with certain models of the Canon EOS bodies. Check out this link to make sure: http://www.astronomik.com/en/clip-filter-system.html
The set of filters I have are Ha (12nm), OIII, SII - $420 for all 3 incl postage
! Bit reluctant to split that set up. Price reduced. Postage now included.
I also have a 6nm Ha EOS clip filter that will sell by itself. They're more expensive than the 12nm ones. $200 plus postage - SOLD
I also have a CLS-CCD EOS clip filter. This is their light pollution CLS filter designed for cameras that have been modded with their IR filter removed. $180 plus postage. - SOLD