Hi James,
I was hoping you would have received more of a response by now. I had used these many years ago in nuclear medicine and don't remember at all where they came from, but I did a Google scholar search and found the top three brands seem to be Olympic Medical (Vac-pac from Natus), Par Scientific (Vac-fix) and Bionix (also Vac-fix). These have been used in a large number of published studies. You might contact the authors to ask for their impressions.