They are available at a few places on the internet. I have had good experiences ordering springs through http://www.springboardsandmore.com/.
If you're seriously interested though, I recommend calling up some gymnastics suppliers and talking to them. Many are willing to come down in price and give you a great deal on shipping. I got a complete package (7x14ft frame, 2-string bed, springs, and pads) for around $500 less then anywhere on the internet, shipping included (which can be up to 300 bucks).
These things aren't cheap, but it will improve your skiing more then anything else. Nothing is better for building air awareness and balance.
way more bounce, it's probably over double the height.
now throw your hands in the air
and wave em like you just dont care
and if you like fish and grits and all the pimp shit
everybody let me hear you say oh-yay-er