Hi there Bob,
You can buy the passes at any metro station (the National Bus Terminal at Albrook, too). The machines take cash and are super easy to use, but there is a window as well, if you’d rather deal with a live person. They may not necessarily speak English but they are, in my experience, really nice and helpful, so everyone seems to communicate just fine. The signs are easy to read and follow. The metro is usually packed but clean and speedy!
Best,
Jessica