In the UK, our guidebooks to Scotland, the Lake District, Peak District and Snowdonia are readily available in their regions.
In some places you should have no difficulty at all. So in the French Alps, Dolomites and Switzerland you will often be able to find our guides that cover the areas. Other areas are harder for us to get our books into, although we work at it all the time.
However, we would recommend buying the guidebook before you leave, firstly so as not to be disappointed if it is not available locally and secondly so that you can use all the planning information included in order to get the best from your trip.