It appears that the term "moleskin" is tossed around a little freely, and you'll have to really figure out what the heck it is.
A company like Nazdar will check it out and suggest their best product, perhaps a solvent based air dry ink.
I remember when I started out I tried to be all things to all potential customers before zeroing in on apparel, or at least similar materials.
Frankly, I was in a small place, and didn't have the room to stick with the various flat stock substrates, especially those requiring air drying on racks.