Good luck! The cups always broke before the plates!
Have you tried replacements.com? Patterns of the Past?
There are lots of sites dealing with discontinued patterns. And don't be looking for cups for snack sets.....a tea cup will work. and if you can't find them....a simple glass cup will work.
Linda C

Here is a link that might be useful: discontinued china sites

Never heard of "tennis" sets. Assuming you mean some kind of plate with a specific place fore a cup... kinda like for punch?? My SIL collects them and uses them mainly for holiday gatherings. Cups aren't really practical for a drink, so she uses them to spoon dip into for veggies or cocktail sauce for shrimp.

Replacement.com is expensive. Being frugal, my advice would be take one plate with you and check out thrift stores to see if you can find something to fit the hole.

The term Tennis Set is commonly used for sets in fine china, the glass ones seem to be called snack sets more commonly.
they were meant for cake and tea or coffee or a small sandwich and tea.
And yes replacemnts is expensive....but if they have what you want...!