nimbus wrote:

I am looking for any technical document related to the SNEFA Attitude
gyros.

Where in Eruope, could I let it maintain?

Your chances may improve if you spell it correctly: SFENA. :-)

SFENA was a major French avionics company and its horizons have had a
good reputation and have been very wide spread in France. I think
virtually every European avionics maintainer will be able to help you.

BTW, SFENA as a company does no longer exist. Its successor is Thales
Group http://www.thalesgroup.com/ (complicated story extremely simplified).