Drivers side seat belt locked in place after a crash

You're right. Many of them use an explosive charge to tighten them during a crash. Start by checking at a few local salvage yards for the correct color and application.

YouTube is full of videos for every make and model. Basically, there are plastic trim panels that snap apart, and the rubber weather seal around the door opening must be pulled off. Those show how to remove the seat belt assembly.

There are also some that show how to take your mechanism apart to unlock the belt so it can be reused. I strongly advise against doing that. While the belt will work the same way they have since the mid 1970s, you will no longer have the pretensioner feature that works in conjunction with air bags. In the event of another crash in the future, especially one involving injuries, you can be sure an insurance investigator or lawyer will find the disabled safety system, and the person who did that could find them self part of a lawsuit. Also, you'll see there is a bright yellow electrical connector plugged into the assembly. That means it is part of the air bag system and as such, it is monitored by the computer. The missing explosive charge will be detected, a fault code related to that will be set, and typically the computer will turn the system off, and turn the warning light on to tell you. That may result in the air bag not deploying in a crash.