Originally Posted by dddd

Since many French parts were formed from steel sheet, I usually look for an all-steel, generic derailer without pronounced branding when looking to replace the plastic ones.

Note that you likely may have to shim the seattube clamp to fully grip on a French bike's slightly-smaller (Metric-sized) tubing.

Here's one example, 1979 UO9 Super Sport with a steel DNM front derailer sourced from shop discards. Works well, though I have to admit that even the Simplex plastic front derailers have always worked very well for me in dry conditions, even for spirited riding in these foothills.