Spring can unlock it for you if you meet their terms.
"To get the software programming code or "lock code" for your phone, upon deactivation or after deactivation of your Sprint phone, the following things must be true:
The phone you are deactivating or have deactivated must be a Sprint phone.
It cannot be a Sprint Global phone (international phone).
It cannot be a prepaid device.
You must be up to date with all payments to Sprint, and otherwise not in default of any obligation to Sprint under the Terms and Conditions of Service.
If you're a former customer, you must have completed your contract term with Sprint, and at the time of deactivation, you were not in default of any obligation to Sprint under the Terms and Conditions of Service, including payment obligations.
If you meet these criteria, dial *2 from your Sprint phone or 888-211-4727 from any phone."
https://www.sprint.com/en/support/solutions/device/faqs-about-unlocking-your-sprint-device.html