Thomas Scientific reportedly has Eupergit CM to sell. There are several varieties of these beads and I believe they are made by Sigma/Millipore which makes the fact that Sigma no longer seems to sell them all the more puzzling. Perhaps they are being phased out, luckily there are many alternatives, good luck!
I worked on Euppergit C 250 L during my master thesis and it was quite old. I think it is not available for sale now. I recommend you to try Immobead 150P. It is an improved version of Eupergit C in terms of the number of epoxy groups