Do you mean crosslide or topslide? I think there would be quite a high probability but crosslides are not often sold 'loose'. Also look at Drummond parts. A starting point would be to list the pertinent dimensions on here and see if someone will add the equivalent for a few models of Myford.

If the screw goes through the casting then you need the saddle anyway not the crosslide. IT all looks like a copy of the Drummond. However the saddle is less likely to be a good fit on your bed and is probably just as worn as yours.

There are three main areas contributing to the backlash.
1. the setting of the screw and the handle and nut (I'm guessing it is the same as the Drummond and ML1 ) This takes some care and is often worn and scored. Thin brass washers might help improve the wear surfaces here.
2. the variation in wear of the screw itself at the middle compared to the ends. You can measure this variation with a DTI.
3. The wear in the 'nut' which is part of the saddle in this case. This can be sorted with a backlash adjusting nut. This is a small brass nut say 1/4 inch so two threads which can be quite a sloppy fit. Put this on the outside face of the saddle 'nut' and with the screw at the least worn section do up the brass nut to lock it all up. Back off a tad to free it up and lock the brass nut there so it can't rotate. You will need to use some ingenuity for this.