Have you tried a 24mm post? 0.2mm difference is pretty small and those old Peugeots usually have a seat tube with a tapered seat clamp, so you only need it to fit in the clamp section rather than the whole tube. They’re not exactly precision made. It might easily slot in. And if not you could turn it down on a lathe easily or sand it down yourself with little issue.
Have you tried a 24mm post? 0.2mm difference is pretty small and those old Peugeots usually have a seat tube with a tapered seat clamp, so you only need it to fit in the clamp section rather than the whole tube. They’re not exactly precision made. It might easily slot in. And if not you could turn it down on a lathe easily or sand it down yourself with little issue.