With the MK2 you can fit the Mk3d/Mk5 slider, but not the MK5g. Correct me if I'm wrong, but I believe the 2, 3d and 5 are all analogue pitches while the 5g is digital.
If you're in the UK try Bop DJ
or Dj Spares
as I have found their prices to be better than Juno.
Dj Spares is also good at answering questions like the ones you have asked (he is a tech with experience of repairing/servicing dj equipment).