That's a porti potti, not a cassete toilet. I worked at an rv dealership in the parts dept here in Canda and was unable to find a distributor who carried one. You may need to ship one over from the UK.
This is a cassete toilet
http://www.homesteadcaravans.co.uk/imag ... Toilet.jpg
They seem easier to use than a porti potti. It is not fun carrying a container of poo through your living quarters. I like the idea of cutting an access for the removable cassete so you can empty from the outside. The best part about these systems is you can empty them at any bathroom. However you do get some odd looks from other patrons when you walk in with a big plastic box.
I don't miss ours at all.