Same place as everyone else ....online.

I have found a few bikes in the street though that have been dumped.
In france it is normal to put your unwanted items in the street for people to help themselves.
Officially you email or phone the council and they come and collect it but normally the items have already been removed.

Two weeks ago two buildings down were clearing out there there caves and i got four bikes.
A 650b ladies step-through a 1970s mixte a 90's no marque ladies mountain type bike and a vintage BMX.

We have collected various bits of furniture this way as well.

It's a good way of recycling! I give the bikes, i get for free, a quick tune up making sure everything works well and replace the cables if needed etc and then sell for a cheap price so someone still gets a good deal.

Also i have always been good at finding items for good prices.

Most of my nicer bikes have come from Leboncoin or french Ebay though.