I got all the bits I used from http://www.tandyleatherfactory.co.uk in Northampton and http://www.theidentitystore.co.uk in Matlock. They both do a great mail order service or you can visit them to pick up what you want (I can vouch for them being very nice people in both, as I visited both places this week). http://www.leprevo.co.uk is another shop but I've not personally used them.
I also found http://www.kingsmerecrafts.com was a great resource and even has a downloadable PDF template for a tankard but I ended up making my own as I made the base differently. http://www.leatherworker.net is another good place to look for ideas.
Finally of course YouTube has been a godsend to me helping me learn the basics of saddlestich and giving me all sorts of other ideas.