You might want to try looking at the parameters from the Nacra model line - although I think you'll find that finding a perfect fit is not going to be easy. The Nacra 6.0NA has a large boomless sail with the track - but it's probably too deep and the track would be too far aft. One thing is for sure - you will have a lot of headaches trying to get a sail to fit (and perform reasonably) from another boat. The Inter boats all have booms.

On the other hand, any sail manufactuer will be able to put together a new sail for that boat. You can expect a good sail from a reputable catamaran sail maker to cost around $1200.