Hi, I was browsing internet for this exact information. I think I have the coin you describe. It has a rooster on the reverse with the word Gallia around it, then a circle of dots and the word Vercingetorix around that circle. There is also a sickle and an oak leaf. The "coin" seems to have been made of two separate sides.
I inherited this medallion from my grandmother who found it - some 60-70 yeas ago at least, in Warsaw, Poland. It has a little hook and I used to wear it as a necklace.
I agree with your comment about the similarity to the 1865 monument erected by Napoleon.
Any more information would be greatly appreciated!