If your bike has Stronglight model 93 cranks, it will go down to a 38T with stock chainrings. Red Clover Components offers a reproduction of the rare, never-catalogued 37T chainring, but they're spendy at $150 a pop. They also sell a 42T triple-izer chainring which would allow you to fit a granny ring, but that would necessitate swapping out your crank spindle from the likely 118 mm to a 125 mm - those are out there, they were stock on the Raleigh Gran(d) Sport(s) that used the model 93 with an alloy chainguard in the outer position, 52T on the inside and spacers and longer bolts to hold the 42T in what would be the granny position. I am assuming you have the correct crank tool for the Stronglights with the 23.35mm threaded section, yes?

For a while in the late 90s I had a PX-10 set up with a 38T inner ring, and had I had a lick of sense I would have kept that rascal.