More info found. In 1970, the last religious inhabitants of the monastery moved out. In the same year, the city of Bourg-en-Bresse established a "municipal service for culture
" (OMC) with a mandate of i.a. organising an annual cultural event (doc 531 W1). This eventually turned out as the "rencontres de Brou". However, in 1970, funds were needed to fix up the place so that it could be used as a museum and for events.
The only 1970 manifestation I found was a theatre week (May 11-16, 1970). It doesn't look like a good candidate to have instigated this token, so my speculation is that it was used for fund-raising for the restauration of the monastery.