Beginners questions. No. 2 - where to buy from ?

I've been paying attention sitting at the back of the class and I've even done some homework as well so I've progressed from knows nothing to knows a little bit so my next question is - where do you buy these GPS machines from ?
Are we talking the likes of Amazon or this GPS warehouse that I've come across or are there proper shops around ?
I'm in la belle France nowdays which may complicate matters postage wise but we're coming over to that London town, and probably Milton Keynes as well, on a flying visit (actually I lie - we'll be on the train) in a few weeks so if there are any "normal" shops about that may be an option.
Hints and tips appreciated, thank you kindly.

Get a Zumo from the cheapest place you can find. Garmin's technical support is (in my experience) very good so should it go wrong just send it back to them for repair etc....

I have used GPS Warehouse a few times and prices seem good and delivery next day.