You've come to the right place for leads.
If the moon and stars all line up, your friend might be able to find an original bolt, but what are the odds of that happening?
I would guess that your friend will have to find a gunsmith/machinist who can either repair the broken bolt, or fabricate a new one. The odds of finding old school gunsmith who can do this are better than the odds of the planets aligning up.
Try this forum-->>>
https://winchestercollector.org
They have a forum where people can post questions regarding restoration, repairs, etc. If your friend posted his needs, perhaps someone there would be able to direct him to someone who could make or repair his bolt.
>>>>
https://winchestercollector.org/forum/restoration-repair-and-maintenance
Call this guy--->Winchester Bob, (207-532-9206), he specializes in repairing old Winchesters, although I didn't see anything to do with Henry's on his website, (the oldest Winchester he lists is the 1864, but perhaps that bolt fits the 1860 Henry?), but he may be able to give you a lead or advise. Or, he may be able to fix your friends Henry. There can't be that much differences between the Henry and Winchesters.
website-->
http://winchesterbob.com
To learn more about his Henry, look at this website-->
https://www.rarewinchesters.com
Your friend could also give them a call to see if they can offer any help or advise. They do have a pretty good amount of info on the original Henry's.
I wish him all the luck he needs to get the gun back in working order.
He can repay us for our advise by posting some pictures of his gem on this site, and letting us know when he gets it fixed.
edit-- I see where Uberti makes a reproduction 1860 Henry, and replacement parts for them are available at Numrich Arms. Their website -->>
https://www.gunpartscorp.com
I would think that the Uberti parts probably would not fit in an original, but you never know. Perhaps with a little bit of modification they would.