i don't know the builder, but that looks like a pretty nice French randonneur / porteur frame. It's most likely designed for 650B wheels. It's made for a chainstay-mount derailleur (which would bolt to the tab in front of the drive-side drop-out) with an external tensioning spring that connects to the loop on the drive-side chainstay just behind the bottom bracket shell:



looking at the braze-ons around the BB cluster, they're intended for mounting a chain guard. Lack of a front derailleur braze on indicated that it either didn't have a front derailleur or used a clamp-on model. either way, it was probably rod-actuated as opposed to one controlled by a lever and shift cable. Crankset would be cottered, probably an RFG, Duprat, Nervar, etc.

Brakes were probably an old style of side-pull like LAM. Would have had fenders and racks as well.

Where to find this stuff? Ebay.fr (ebay france) is your best bet. It will be pricey, especially the derailleurs and wheels. I have actually hoarded up nearly all the parts for a restoration of this type and could be convinced to part with them if you're interested. Or you could go the cheaper route and slap a 3-speed SA hub on the back and call it done, it wouldn't be out of place for the period.