Well, if you know what you are looking for, you need to go to an electronic repair and supply shop. Find one who caters to electronic technicians, because you are correct...... Radio Hack won't cary what you need. There should be a big 4 digit number on each of the MOSFETs along with a letter. If it says C4120, you need a 2sc4120 output. If it says D1861, you need a 2sd1861. Now, like I said before, they must be replaced in pairs. So if you only find three shorted, replace the other good one in that channel. There are 2 in each channel (one for the B+ and one for B-, usually around 40 volts for 12 volt power supplies). They should be no more than 20.00 each. Did you check to see if the emitter resistors are open? Those are the big white ceramic resistors on each channel, should be .22 ohm or equivalent. Those are exactly the opposite of transistors. If they measure short, they are good, and if the measure open they are bad. You should double check them to be sure before replacing the outputs. If an emitter is bad, it will blow your new outputs the second you power it up. They don't open all the time, but I always check them because they do open occasionally.