Store that sells flour for baking in Puerto Rico

You may want to try Napo Velez chain or MrSpecial.

I do !
1.- Health food store (Adventist )very price though.
2.- El Viandon in Mayaguez
I'll say is almost next door of the VA clinic
At the same of the VA the building is like warehouse.
www.elviandon.com
Phone 787 265-5148
They have all kinds of gormé things. Black quinua, cardomom, black truffles,etc all kinds of flours. Various eatable flowers, and mini greens. They supply to several restaurants around Mayaguez.
Hope this helps if you have a German bread recipe please share with us.

I have found limited staples like these at the Super Max in Dorado.  My son is gluten sensitive -- so they have the best selection I have found thus far.

I would try Freshmart, they have a handful of locations, perhaps message them and ask which store has the most variety.