There is a list of probabilities of salvageable items at each salvage point in the fan made guide.
Spoiler Alert: If you want to enjoy the game without spoilers I would not recommend looking at the guide.
Also, the guide is updated as the game is updated as well.
https://drive.google.com/file/d/1Q_5mCZTfUktk5-g5E-d7Ut78hQuXiSjO/view
There is a 5% chance to get a scrap metal at the mess hall. The guide refers to it as cafeteria if you want to look for yourself. Page 40.