mount_ufs is *not* in /usr/sbin.  it's in /sbin - on the root 
partition.

if you just upgraded with aug binaries, boot netbsd in single user
mode and check the /sbin partition.  if mount_ufs is not there, you
need to re-extract the sbin.tar.gz binary archive onto that root partition.

It sounds like maybe you never extracted this archive in the first place.

Good luck!

-- dick __ __//___________________________________________________________
Richard H. \X/ood                                        dwood@rhw.pic.net
246 Bancroft Drive,     Garland,  TX   75040    USA        +1 214 530 2595