French breakfast cups

Try the BHV department store on Rue du Rivoli, it has a good housewares department with lots of very nice dishes, on one of the upper floors. Conveniently located across the street from the Hotel de Ville on Rue du Rivoli. Monoprix is good - a bit more basic, but they have cute stuff.
Most souvenir shops are likely to have them, but they will have tourist oriented designs, and not fine quality -- probably not what you are looking for.
Walking around the city, you are likely to pass by many other stores that will have them, and if you happen upon an interesting outdoor or flea market, you may find them there also.

I was at the Giverny gift shop in June, not sure I saw anything like this, but wasn't looking for cups. They had nice stuff though.
Good luck.

If you are in Paris on the weekends, head for St Paul Village, which has some very pretty china and faience cups. Most of the shops are on the street, instead of inside the courtyards, some may be closed for vacation.
I presume you don't want the usual "bols" - but those can be found along the same street at "La Bonheur de Chance".

What is a breakfast cup? I'm not familiar with that term. Is it the large bol that we loved every morning of our stay in Provence? Or the large (handled) cups for cafe au lait?

Probably looking for tea cups - fine china or faience.

In Brittany, they drink their morning coffee from a bowl.

do you mean decorated egg cups?

And here I was assuming a cafe au lait 'bowl' as tea cups can be found anywhere. Perhaps the OP could clarify.

Look at Galeries Lafayette. They have a whole section on china. Printemps Paris-Haussmann probably does too.