I am not sure about the basic "Sculpey" brand for general use or for polymer clay beginners... I can still see that around, but the one that is
definitely off the shelves is the "Studio Sculpey" range. This one:
What we have instead, apparently, is the new "Sculpey III" brand or "Sculpey Premo" which apparently contains much less plasticizers than Studio Sculpey. I don't hear anything about those being discontinued, fortunately, because Kato and Cernit are not the easiest clays to get here in the UK, and I can't stand FIMO. That leaves me having to try this Sculpey III product because there are no others with the wide range of colours and wide availability like Studio Sculpey used to have. But they are sold in smaller packets than Studio too, so I suppose it'll work out more expensive anyway.
I'll have to ask other sculptors I know about ordinary "Sculpey" brand and whether that is being discontinued as well, although I have not tried that one myself because I hear it's not the best quality compared to Sculpey FIRM, Studio, Premo or III. I have always avoided it because if am making things to sell I figure I should use the more professional and stronger materials. But still, if it was that would leave a lot of people in the lurch who use it, or run classes, etc.
Sometimes it's pretty difficult getting the right clays I need to work with at a reasonable price. America has everything, including all the Japanese stuff for dollmaking, here in the UK we badly need to catch up, even most of Europe has Kato and Cernit much more easily available. This just makes it worse. Some people are saying you can blend two other types of clay to get the effect of Studio, but blending in the end to get what you want usually means there's quite a bit of waste and unused stuff at the end every time.