I am from the UK and have only been boarding at my local indoor snow slope and only since the middle of February.
As I play ice hockey, I thought I had good legs but I guess I'm now using the muscles in a different way??? And I'm going harder and pushing myself as only a hockey player does! ;-)
I'm also guessing that if you are lucky enough to get on the slopes any time you like, and have been doing it for years and years, you'll have trained your body to cope very well???
So, are there any workouts to help me develop the correct muscle groups???
There are several workouts you can do in the off season. Google snowboard leg workouts.
One exercise is pause squats with a little weight.It's the best way of mimicking what your body is doing on the hill. Just put a little weight on your back and do some movements. HUGE results.
Snowboarding or skiing is HIIT, so it would behoove you to do HIIT both on and off season, and keep it going as a side benefit for your heart.
Also as with any HIIT you will benefit from any simple sugar, such as Gatorade or the like.