Sounds like you want a "Dryer vent cap". You can find them separately from the dryer vent kits you have been finding. Any big-box hardware store should have them (in the US at least), maybe they are in a different part of the store/aisle.

You mentioned that your current one may be glued on? If so, use a hammer and chisel/flat head screwdriver to remove the old vent and replace it with the new. Preferably you would use screws to attach the vent to the house, but if it was glued I'm wondering if there was a reason, like the vent goes through concrete and the installer couldn't be bothered to drill anchors for it.