Any FB member can buy access to the CDG lounge as long as the lounge is not very full, not only silvers. So OP just needs to sign up for a FB account and pay 45 Euros. The only difference between FB Ivory and Silver is that Silvers can also use miles.
FLYING BLUE IVORY
You can benefit from the privileged comfort of AIR FRANCE, KLM and Delta Airlines lounges in a growing number of destinations around the world*. Lounge entrance fees vary by airport location:
25 and 45 € in Europe, Asia, Pacific, the Middle East, Africa,
35 and 50 USD in the United States and South America,
30 and 50 CAD in Canada.