In June most salles will be open. As soon as the holiday season starts (early July), then most salles are closed.
In Nice, this club:
http://www.escrime-ffe.fr/Site_FFE/o....ASP?CLUB=7856
Is the biggest one that I know of.
They do foil (which you state is your primary weapon in your profile).
Other than that, check out this page:
http://www.escrime-ffe.fr/Site_FFE/o....asp?LIGUE=502
To see other clubs in the area.
There are no large competitions in France in June or July, except the national championships for division 2, which you have to qualify for to enter.
There are no competitions for foilists in July. You can check the complete calendar for yourself here:
http://www.escrime-info.com/modules/...r=2007&month=7