Audiofanzine is definitely the best place to look for second-hand music gear in France.
You can even set alerts to watch any new “Petite annonce” (= second-hand ad).
FR: OTO Biscuit d'occasion - Audiofanzine
EN: Used OTO Biscuit - Audiofanzine
Maybe only US though: I see prices in $ on Used Audio & music gear - Audiofanzine
Cheers for your help.
I’ll have a bit of a scout around. 
I ended up getting the plugin of this after seeing Alva Noto using it in this lovely recording of his recent orchestral shows:
I tried a few alternatives (Bit Maestro on iOS is excellent but buggy on Mac (it’s not designed for Mac), MBitFun sounds good but the UI has too much going on for me) but really wanted the original and saw a good second hand price.
Very pleased with it on first impressions. The main crushing effect is instant Alva Noto on pads/strings 
as well as crunch on other things, and to me quite a unique bitcrush sound vs. most plugins. The filter sounds quite unique and lovely, smooth. Big fan of the UI too, it looks great and has just the right amount of control for me.
Not sure it’s worth the full price but if they do another sale and you like this sound I’d totally grab it, I think it’s a well executed plugin, especially if you sometimes value aesthetics and a somewhat deliberately limited experience over sheer amount of controls