Second ECU for Experiments: A Guide

Hello,

I would like a second engine control unit for experimentation purposes.
Currently installed (label):
- VW 038 906 012 FB
- Diesel EDC15VM+
- Bosch 0 281 010 651

Where can I get a suitable second device?
From which cars (scrap yards) could I salvage a spare part?

Assuming I have a suitable device, what steps do I need to take for it to function properly in my car (e.g., WFS compatibility)?

Best regards,
CH