Wow, tracking down a complete saddle (and apron too?) that is not needed for the lathe it is on! That will be a needle in a haystack sort of search. I suggest you already have the "parts" machine. You could convert that machine to another application: wood lathe, weld positioner, metal spinning, . . . . . . . . If you are very fortunate you may be able to find a "close enough" similar machine, then mix/match to get one of them working.
I went through a similar exercise with a Maho milling machine (50 years old, uncommon, German) - I had to buy the complete machine (#3000) to get the attachment (#300) I wanted and had it shipped ~3000 miles. Only do that if the machine is a particular prize.
Good luck.