Where can I find the thernistor for McIntosh MC240

You can also try Audio Classics, http://www.audioclassics.com/. I needed the same part a few years ago and they had the actual McIntosh part in stock.

You might try Tom Manley, owner of Statement Audio-Video, in Knoxville, Tenn. Manley refurbishes McIntosh equipment and is one of the top McIntosh dealers in the country. The number is (865) 693-0084. Good luck.

Take a look at Digi-key or Newark Electronics. One or the other (or both) should have it, or an equivalent substitute. The concern would be that something else caused the current limiter to fail (failing electrolytic power supply caps, etc....). Did the main A/C fuse blow? Did any other internal fuses blow? If you intend to "shotgun" the repair, then be sure to get a couple of the limiters as you may have another fail rather quickly. I don't mean to be overly pessimistic, but I've worked around electronics too long. Good luck.