I would contact Elka or an authorized service center. If not a direct fit it may not be all that complicated to have it re-built and correctly sprung/valved for your new bike much cheaper than a complete new shock. I have had Penske units re-fitted for other bikes, see no reason why Elka can't do the same.
Although if it's this one :
The piggyback reservoir will have to be changed to a horizontal unit or remote. As is, if you look at mine you can see it would hit the swing arm.