Jasonb,
Thanks for your post. I went to that fabric store to find fabric for curtains, and your directions were spot-on. The friend I was with who's been living in San Juan for 3 years had no idea it was there, and was thrilled to find it.
One note, they seem to only carry bulk household fabrics. It's perfect for my curtain needs, but I wouldn't consider them a craft store or a place to get fabric for clothes. The staff there was also really friendly and helpful.
Thanks for your help!