In the article on Gap year courses you may have noticed that I didn't actually name any courses or tell you where to book on one. This was because there are many courses out there - some good, some less good, and I don't want to appear to endorse any particular course provider. Having said that, it is probably worth giving you a few pointers to where you can find information, but without any specific links - you can all use Google yourselves.
There are two types of Gap course providers - the official instructor organisations (e.g. BASI) and private companies or ski schools. There is no particular advantage to one or the other, as both put you through the same examination courses at the end of the day. It is worth considering where you want to work at the end of the course, as qualifications will be more readily accepted in the country where they are accredited. If you hope to work in France eventually, then BASI or another Eurogroup qualification (French, Austrian or Italian - all very difficult) will be best.
Look into as many gap courses as you can find. Try the instructing bodies' websites (BASI, CSIA, CASI, NZSIA, PSIA etc.) and also phone them and ask for the course directory - this will have lots of adverts for courses and is usually free. See winter/season workers websites like Natives, snowsport websites and ski school websites. Look at ski/snowboard magazines like Fall Line, Document and so on. As I say, there are lots of options so don't rush into booking the first course you see. Do your research thoroughly and bear in mind that the gap course is not the only way to become an instructor.