Airfields without an ICAO code were given an unofficial euroVFR code, which you might find convenient to use.
For French airfields, this code is built like this:
LFxxYYY
where xx is the number of the departement where it is located, and YYY are the first 3 letters of the airfield name.
Ex: LF42ROA for Roanne Mably ou LF81STL for St Lieu les Lavours.
The euroVFR code is built this way:
EGxxyyy
xx being :
yyy being the first 3 letters of the airfield name.
ex:
EGSCKIL for KILKERRAN, in Scotland
EGSETAN for TANGMERE in the South East of England.
List of all euroVFR airfields with their codes.