Have you tried using 0000 for the PIN2 code? Or see if you can attempt to change the PIN2 code from the Settings menu.
If that doesn't work then you might see if the E71 User manual that came in the StraightTalk package will help, or CS.
Unfortunately there is no firmware that exists online that will bring back the Tracfone APN settings. It was installed at the factory (or possibly wherever America Movil packages their phones) and it doesn't exist in Nokia's servers. Go figure.
If/Since you're using Windows, there Nokia's Configuration Tool that can upload config profiles for the E71. Read through the instructions carefully. That might also solve your dilemma. You will probably need to remove the AT&T APN and MMS settings manually before using the Config tool, just to be on the safe side.
I don't have physical access to the Windows computer I updated my e71 to the latest firmware with (I did the same NNS trick as you and had no hiccups using the config tool post-flash), but I believe I have a config saved with the Straight Talk APNs still. When I can get access to the computer, I'll see if I still have the config setup. If I do, I'll try to post it.