Reponse To Answer
To be clear, when someone posts a question on TR, there is no CV or resume that tells me if they are a 90-year-old retiree or somebody who can create assembly code, so if I talked down to you, I apologize.
The short answer to your question is eBay, but I would think that's somewhat obvious, and if you cannot find anything online, I would assume that you meant nothing for a reasonable price.
To buy a motherboard or case as a repair part is typically triple the cost of a used computer on eBay.
I'm not clear what question you're asking; the issue in this case (no pun intended) is that if your life depending on re-using the pieces parts you have, you could buy a refurbed Dell motherboard and case for probably something like $200 on eBay.
Or you can spend $50 for a similar used PC on eBay, or $300 for a brand new one.
On eBay, a motherboard and case probably costs around $50 as well, so having a known working PC vs the chance of bending a processor pin or killing a RAM chip with ESD is not worth it, in my humble opinion.
I am only trying to help here..cheers.
