As a visitor to Tokyo when I was still back in ol Blighty, every year I would make sure a trip to Tokyu Hands was on the schedule. You can buy just about everything under the (rising) sun here. Everything from Gundams to bags, to clocks, accessories - anything.
For folks living here, Tokyu Hands is also the place to go for DIY stuff. have a look at this previous article on how I got materials from Tokyu Hands to make shelves for my figures.
I remember there being a few decent DIY stores in the UK - although I've long forgotten the names.