The other option is to purchase one off ebay. Search for your model and followed by the unlock code. Most sellers will email you the code within a certain period. Once your provide them with the IMEI number which is located on the back of the phone or found by *#06#
If you know anyone with a tmobile contract, they can request an unlock code for your imei. When they call customer care, the rep will ask for the imei of the phone you're using. The imei can be found under the battery or by pressing *#06# and send on the device you want unlocked. I hope this helps. Cheers!
Since you don't have an account with Tmobile anymore. I would recommend you go online and purchase an unlock code for you make and model as well as the unique IMEI number on the your handset. eBay has plenty of listing. Search your phone plus unlock code. For example, Samsung Exhibit unlock code. Find our your IMEI by going to the dailer and pressing *#06# and provide that during the sale so they can provide you the unlock code. Good luck.