There is a guy on GunBroker.com named Rich [username: rwc] who frequently lists Luger mag bottoms...He might be able to help you...
Or...there is a magazine expert on this Forum who goes under the name of GT...he makes mag bottoms...from scratch...and has some mag tubes as well...he might be able to 'force match' a mag for your dad...
I know - it's blasphemy... 