There are two marques of this name. The first is from 1905 marketed in London by Gauthier & Co of Holborn, UK. These were engine kits with French components so it seems likely they were a French marque with representatives in the UK. The second was built from 1972 to 1980 by the brothers Portal and Jacques Boudet of Villefranche-de-Rouergue.
250cc Sachs 1976 with full fairing, fibreglass bodywork, monoshock suspension, discs front and rear mounted on alloy wheels.
125cc GA Criterium, Randonnée and Quatre Saisons, all with 125cc 6 and 7 speed Sachs engines.
AIM-Gauthier enduro. There appear to have been several versions including 80cc and 250cc, the latter an enduro based on the AIM 250CR.
Sources: srcf.fr, period literature
Could you tell me where I could purchase parts for my 2 vintage 125
cc french bikes called Gauthier powered by Sachs motors ?