There are moulds of many shapes and sizes for many purposes including candle
making on the market.  They are made of a thick white latex -like substance.
Yes, amateurs can make their own and I have seen it demonstrated at the
National Honey Show in London a few years ago.  I forget for the moment the
name of the demonstrator, but he made it look quite easy. Perhaps another
reader will have a better memory than me and get in touch.
Chris Slade