Buy a counterfeit pass from a merchant in the slums. You can technically try using it to get into UNA but the success rate sucks. Instead, bring the crappy counterfeit to Lin-Lin. She'll either upgrade it for you or tell you where to upgrade it I can't remember which. Use the upgraded pass and you'll be able to enter UNA no problem.
After paying for the upgrade once you can make quality counterfeit passes yourself for a fraction of the cost by combining a crappy pass with a pen. The success rate for that depends on your nimbleness though so you'll probably want to grind it if you're low.