Suggest just keep looking. Last year I thought I was going to strike out big time here in Syracuse, NY. I just kept looking and ended up with a few sources. IMO you've done the hard part already. You will eventually find the pine bark.

When you talk to orchid suppliers, ask about seedling bark. In my experience, it is usually a good size for gritty mix. Though you should certainly check it out yourself before purchasing.

I buy 20 or more bags of pine bark fines in Texas every year in Dallas or Midland/Odessa. San Antonio should have similar products available. The big box stores almost always have it, but it will be labeled "soil conditioner" or "landscape mix". Your problem may be that it is mid-winter and the stores haven't restocked for the next growing season.

I get mine from Lowe's labeled as landscape mix that you would have to use 1/4 (or is that 1/8th"?) screen to screen out fine stuff from landscape mix. Pretty cheap for 3 cubic feet bag which I think costs 3.50 dollars.