Just to let you know you can buy a freshening up kit, consisting of new cassette, lid and seat.
May we be impolite and ask why you need to change out the whole toilet?
We louvre a good toilet thread!
Try CAK Tanks (caktanks.com). They appear to stock all parts for yours.I cant find a replacement cassette for it , ive tried the thetford web site and there does not appear to be one for a straight swap
the one that I had as the numbers
model cassette c-402x r
ive tried to find a replacement cassette , if anyone can help on that id be a happy chappy