@roger,
ski jumpers start with liking moguls . I always tried to ski around em unless I had to get over something. The old NASTAR slopes used to have a small jump area. The Olympic places like Lake Placid once had two or three different sizes (like diving boards)
Heres a picture of the Lake Placid ski jumping training areas. The ski jump areas are in two valleys with about 4 different size jumps. The actual training for jumping and "Hot dogging" use these pools. I don't know if one can just "show up" and try their hand. The freedom from Liabilities do absolve slopes from the inevitable broken bones and necks but people still sue, so I think the "gatekeepers" are some affiliation with a jumping school