You don't need to be, you have studied there or graduated from there, therefore you're an Alumni, and you can pay the fee and get access as such. Independent researchers pay for access to other libraries to best suit themselves. They're all a little different, but research libraries will have some way you can create an account.
Check out the details of your old University library for Alumni access or Researchers access.
You might get lucky; some have bursaries for unemployed, etc.,