Austin Kayak sells them as well, but I don't think anyone rents them but maybe REI will.
Big Bend is very safe and very isolated but that didn't stop them from posting a lot of Border Patrol there and the NPS hiring a lot of additional Law Enforcement (LE) rangers who really don't have much to do but Homeland Security money is paying for them. There are something like 35 LE rangers for a monthly visitation average of 25,000. Increasing reports of overzealous and bored LE rangers in traffic stops and such. They are also the ones who are responsible for making sure you have a bear canister or not or at least enforcing the rules. It is those kinds of tensions I was referring to.
They have been trying to enforce bear can rules over the last several years even though it was not a written rule anywhere, now they have at least made it official but again only found in the Superintendents Compendium, published no where on their website or other materials.
They probably will not approve the Ursack in their final list because they do not want anything tied to plants (bear hangs and hammocks are not allowed)