This is the info listed on the Milwaukee Tool site, I went to the files and scrolled down to each parts breakdown to get the part numbers. 14-46-0594 is the 1/2" arm assembly and 14-46-0596 is the 3/8" arm assembly. If you search those numbers on the web if someone other than Milwaukee sells them you should find it. documents.milwaukeetool.com/54-38-2485.pdf documents.milwaukeetool.com/54-38-2480.pdf
Ahh so the head is probably the bigget chunk of the expense, of manufacture. As the body bar a few bits looks like all the others. Hmm I could see me wanting both heads. But the cost of two bare units. Tough choices