Not sure why you think you need to do a course.
What are you expecting.
I suggest you go snorkelling round the coast first, then decide if you want to go spearfishing. Unless you can dive to about 10m+, hold your breath for 2 mins and swim for miles, I don’t reckon your wish will live up to reality.
I used to do a lot many years ago abroad, Ive also spent quite a bit of time diving the UK coast. I wouldn’t bother doing it here in the UK unless I had a boat and lived on the coast.
I wouldn’t bother doing a course either, you just need to try it for yourself. Get the right kit (hard in the UK, French dive shops sell it). Then just find somewhere that’s not a marine protection zone and make sure there are no bathers about. Then spend hours diving down, trying to stalk wary fish that are too small to bother gutting. You will also need to be able to identify fish. You will need to be able to shoot to kill so a wounded fish doesn’t escape.
Unless you get deep for long and out on a wreck site you are unlikely to catch anything that’s worth eating.