They appear every now and then on ebay uk. The characteristic pin rather than keyway slot marks them out but a couple of other rarer lathes did use the pin mechanism so just occasionally you might get a different one. Main thing is they are 14 DP So will not mix with Myford or Boxford ones. If you have none at all then you could consider using the alternative.
Myford ones are 20DP so would be smaller and use a keyway rather than a pin so some adaptation would be r'equired, and sometimes you might need to put in an extra gear or two to fill the gap.
Have you joined the Drummond yahoo group and seen Tony's site.