I buy my animal glue, which I use for woodworking, from shops which specialise in tools for cabinet makers etc. Two shops which come to mind are: Messingers in Guildford Surrey and Buck & Ryan in Tottenham Court Road in London. Alternatively you may be able to obtain the glue direct from the manufacturer:
Liberon Waxes Limited,
New Romney, Kent, TN28 8XU.
The glue these days is in the form of little beads. I buy "Pearl glue" but I think there is another variety, perhaps finer called "rabbit glue" if I recall correctly. When I was a boy I bought it in "cakes" ie slabs about a quarter of an inch thick which you had to break before placing the pieces in the glue pot to boil. The smell is wonderful.