None of my French bikes will take a 22.2 stem. The Stronglight top nuts will allow it, but the steerers won't.

If it's a seventies PX10, the BB threading is French.

You need to be aware that a seventies PX10 will have Simplex dropouts and will only accept Simplex derailers without modification. It never fails that someone will post that all you need to do is tap the mounting hole to 10 mm X 1 mm, but there's more to it than that.

Your seatpost will probably be 26.4 or 26.6. A correct Simplex post may cost more than you paid for the bike.

All of my bikes were built with parts from eBay. Obviously I don't agree that it's a horrible place to get parts.