I have a collection of European/South American/Asian/Australian OO/HO, every one bought in that country.
Norway - Sweden - Denmark - England - France
Belgium - Luxembourg - Holland - Switzerland - Austria
Italy - Germany - Australia - Japan - Argentina
USSR
The only countries that I have been to that I have not bought a train are
Greece - I've seen Greek models in other European countries, but not in Greece
Finland - Same as Greece, although I only had time to visit one shop in Helsinki who was out of trains.
Singapore/Malaysia - Same as Greece - The train store in Singapore had lots of European and US, but was out of the one Malaysian model they normally stocked
Ireland - A quick trip and although the train store was about 6 blocks from my hotel, I was there on a holiday weekend and the store was closed
Poland - Only had 3 hours free while on a business trip in Poznan and didn't find a train store
Hungary - Saw Hungarian trains, but since I was taking a Romanian train from Budapest to Vienna, I bought a Romanian Coach like I was taking.
Russia (Under Communism) - Bought a TT East German Railcar in a Department Store in Leningrad (now St. Petersburg)
Iceland - A country with no active railways and no commercial models as far as I can tell.
Bermuda - Same as Iceland, although I bought a Bermuda railway sign and book at a shop in Hamilton.
As for a layout, I have a board with 3 loops of HO track (18" radius, 15" radius, 8"radius) that I run the OO trains on.