You can get reservations for France also via other companies than via Eurail.com. 

Online possible also via B-Europe, where you can book for 2 people in the same time (reservation fee 10€ or 20€ + 4€/boking). You need a paper pass cover number. For mobile pass generate here your cover number: 

There are several ways to make reservations for French trains.

You can call  b-europe and make the reservation. 

The phone call is rather expensive.

https://www.b-europe.com/EN/Contact/Contact-Centre

Another way to make reservations for French trains is to call SNCF.

https://www.sncf.com/en/customer-service/contact-us/telephone

 Press #85 for English, no booking fees, reservations are sent via e-mail. Not all credit cards are accepted.

For domestic French reservations, you can also call NS. Also no booking fees and they do accept VISA. Remember the country code (+31)

Thank you both (Angelo and AnnaB) for  your ideas. The b europe website worked for some seat reservations but I got error messages when trying to pay for two other seat reservations. So I ended up calling the b europe site to complete those two.

In retrospect, it would have been much easier to purchase the tickets themselves rather than buy a Eurail pass and then have to purchase the reservations, and probably less expensive when you take into account the charges for the long distance international calls and the seat reservation fees.

Also, I was unable to get the b europe website to work to purchase seat reservations using a Mac computer. I was able to get it to work only using a PC computer.  

I hope this information will be helpful to others.