You are not going to find any seats for it, but check with your local Briggs Plumbing fixture dealer and see if they still make the conversion kit that allows you to use a conventional seat on it.
There are no color seats available, but we do stock the seat for the Case 1000 in white. This is the only color I have been able to get, they are not cheap but it’s the only option unless you want to change the toilet. If you need more info go to our web site and email me.