Michael is almost right - there were 38 cars sold, and 41 manufactured. Two were crash-tested, one remained in the DeTomaso museuem. Actually, now that that has been sold, the total number of Pantera Si cars sold is now 39!
There is one for sale that I know of - in Switzerland. It only has 400 miles on it - if it is the car I am thinking of it still has the plastic on the doors, and is a targa. They are asking 149,500 swiss francs, which according to Yahoo is roughly $117,000. Contact Fabio at pimout1@prodigy.net.
There's another one advertised for 125,000 euros in Germany. Go to
http://www.mobile.de, plug in DeTomaso and you'll get a dozen hits. A nice Vallelunga, and an Si. It's all in German so good luck!