Alk8944, I was the one who mentioned the 313631. It did exist in the Lyman library of moulds, but only for a very brief time. They may be found with a quick search of the Internet and one or two of the boutique mould makers have cloned them. I prefer the ones with plain bases, an improvement over the original with GC, IMHO. You may well find them worth giving a try yourself!
Froggie