MGA has a 3rd party lounge. It has never been offered to me, and I have never asked, so I assume it's not affiliated.
I also find that SJO borders on being in this category. One free drink or whatever and then anything else comes with a bill, in an environment not much different than the terminal. SAL is similar.
I didn't think ASU had one, but the lounge finder link says that now there's a contract lounge.