Where do I get cleaning tablets for my schaerer...

Question

I have recently purchased a second hand schaerer opal and am very happy with it! It's time for a clean though and the manual tells me about a two coloured tablet and I haven't been able to find these anywhere!!! Does someone know where I can purchase these special tablets or if there are any others on the market that I can also use with this machine? Thanks heaps for your help and efforts!! Sigrid