I've just put together a list over 600 UK suppliers of plants and seeds - no tools, gadgets or other "essential" items and all suppliers offer their plants or seeds by mail order (or did when checked).

It's better (well I would say that wouldn't I?) than the RHS Plant Finder in that it includes vegetables and some very small suppliers (but you can't find individual varieties on it)

It's not commercial!! It's at http://www.plant-seed-mailorder.org.uk