[raymo]

If you can't find the nut, and have access to metal working equipment,
you can put a helicoil into the nut, and if necessary, onto the male
thread as well. If you can't do it yourself, any machine shop will do it
for you, at only a fraction of the cost of another mount.
It just occurred to me that they may not make helicoils in that fine a pitch thread, and would have to put a coarser thread on both the male and female parts, but it wouldn't really matter.
raymo