Velo-Orange sells french cartridge bottom brackets, which I'd go for. Or, like someone said, take it down to a bike co-op and rebuild it from used parts. I'm assuming you have cottered cranks, so yeah, upgrading to a more modern, square taper, would be a good idea. Make sure you screw in that fixed cup crazy hard though, the french threading tends to make it unthread itself (at least in my opinion.)