If you have trouble finding one here, you might try the eBay seller "astrosmith22", in Japan. He frequently offers sets of Horseman cams - perhaps he can find a 150 for you.
At one time I needed an extra cam for a 105mm Horseman lens. I borrowed one and had it duplicated at my friendly neighborhood machine shop. Since a lot of the cost was setting up the computer for the first one, I had them cut out about 5 others which I "disposed" of. It worked fine and everyone who got one of the extras was pleased also. For small jobs, the shop let some of the employees take them on after work for pin money. A tip of a bottle of bourbon, donuts, or even a case of Coca Cola for the shop helps you get a foot in the door the next time you need something...This summer I picked up my project on a hot day, paid for it and left them a watermelon! )
--bob
I contacted "astrosmith22" through his eBay listing and we have made a deal for a Horseman 150 mm cam. He did not have those little Horseman Release Adapters # 25533 that I also need. One day somebody needs to make a dozen of those, maybe even me.