In London there are three main suppliers which I use, all based in
Hatton Gardens, which is the city’s jewellery centre (and dead handy
to my office).
have a good selection of tools, metal and bead stock, and allow you
to wonder around and browse their stock. If going, it is worth timing
your trip to miss lunch, when they are busiest.
have an wide range of tools, metals and stone stock, but you really
need to know what you want and what you are doing to get the most out
of them. Their catalogue is particularly good.
excellent range of tools, no precious metal stock though.
There are a number of others about which I use occasionally (Lynco
for bags and boxes, Samuel Findings for cufflink backs and Euro
Findings, but not sure about their web presence and catalogue sales).
Hope this helps.