Advice Needed Anyone know how to obtain inactive instagram usernames?

The only way to obtain a name that is not used anymore is by starting a company with that name. Make other social media accounts with that name and contact Instagram that you need the name for your company. They will review your question and there will be still a small chance of getting it.
But yeah, sometimes DM'ing the owner of the page works too. Some will give it to you, some will sell.