Most hospitals hang onto their exam tables until they are incredibly decripit. They almost never dispose of equipment directly. Rather they have a surplus wharehouse where they send useless equipment for other departments to pick over. Finally, when a piece of equipment has sat in surplus long enough it is consigned to auction. These are held anywhere from once a year to once a month (depending on the size of the hospital). Equipment rehabers purchase from these, restore the equipment and resell it. Thus you would have trouble picking an exam table up used. And most likely, even if you got one it would be likely to be missing the stirrups as any usable parts are stripped off before sending to the surplus wharehouse.

As your wife has noted, stirrups are nice things to have to help support your legs and even better are the knee supports used in obstetrics. Otherwise the bottom has to support her legs up in the air, so to speak, in a less than comfortable position.

I might consider figuring out a way to affix, in detachable fashion, a post to either side at the end of the table. These posts should extend upward of two feet (60 cm) above the surface of the table. You can then fabricate line to suspend from the tops of the posts with loops in the ends (do you know how to execute an eye splice in three strand line?). The sub's feet can then rest in the loops much as with stirrups. When not required the posts can be detached.

Hope this was of help.