according to Sheldon Brown's
handlebar cribsheet, the older French standard was a 25.4mm clamp diameter for bars. If this is what's on your 1972 Motobecane, it will be difficult to find a replacement. However, you could file the interior clamp of the stem and use the much-more-common 25.4mm-diameter bar.
Also, it's possible the stem works with 25.4mm bars anyway.
Not sure on the pedal threading. Maybe post this question in classic-and-vintage forum if you don't get more help from the mechanics forum.
If it's going to be too too much work to upgrade stuff (e.g., if you have to replace the stem to get newer bars, but maybe the stem won't work b/c the internal diameter of the fork's steerer tube is a weird size, or if you can't go with modern pedal threadings) then maybe it's better just to get a diff bike.