If you are sure that the problem is just that missing transistor then try to find a used or refurbished version of the same motherboard. That motherboard does not necessarily need to be working - it is just a "donor" for parts.
Look at the other transistors as well. A matching/identical transistor could be used elsewhere on the motherboards.
There may or may not be some markings on the transistors or boards so you can compare boards and transistors. With some hope that the components are the same.... May or may not be true.
If identical, desolder the transistor from the donor board and use that transistor to replace the missing transistor.
Requires soldering skills, proper equipment, and a clean working environment.
No guarantees that the replacement will work.