I sometimes forget not all towns have a friendly saddlery who will sort you offcuts in exchange for biscuits.
Otherwise, a decent fabric shop will have a couple rolls of leather. £10 got me a about a square meter of 5mm thick leather for something else I was fiddling with.
Hi shop, can i have a square of leather please :P
I honestly have no idea where to find a small piece of leather thick enough to work, i was thinking more along the lines of some canvas sewn together