have a look at;
http://www.farriermarine.com/sails.html

An F27 sail seems to be about the right proportions. If you cut it off at the 1st reef points, i think it will still be a bit big, so will need cutting higher and tack and clew eyes fitted. but you might get lucky and find one with a reef point in the right place.

Sail will be a bit heavy for even a P-cat, but there must be lots of old ones about that will be cheap.

If you like, give me some of your details and I will post on the Farrier owners site and see if there is one for sale in your area