Tom, the hard part would be the barrel. I recently found out, that the older suppressors, like from Mac 10's are worthless against the modern stuff, and won't even be taken in, on trade, by dealers, they suggest calling ATFE, and getting permission to demill them. I'm sure, they could be had for 100 - 200 bucks, but still the transfer, 200 bucks after purchase would have to be done. After the appropriate background check, and sign off by the local constabulary. Finding an appropriate barrel that is longer and extends beyond the slide enough, might be a problem unless the factory offers one. Your friend is not going to get what he wants without some dough. Better off to get a good set of amplified hearing protectors to put on, as he grabs his weapon.
My 2 centavo's