There are permanent contract you cans get https://wiki.guildwars2.com/wiki/Permanent_Black_Lion_Merchant_Contract. You can have them in you storage and use them anywhere.They are all listed here, if you want to gamble with Black lion Chests. They may have been a rare drop while playing in the past and I don't know if they are available that way anymore. I got a Permanent Banker a long time ago. There are also some available on the TP for an outrageous amount of gold. That being said, Mistlock Sanctuary is my go to since I got it free with the EXP.