Here's the deal, a "serious" java dev is basically in common terms a Senior Software Engineer, which goes for different rates based on region or personal shenanigans. Usually it's 3k EUR+ for a month of work (22 days).
So the answer is - you can't find serious ones because the pay / your profit from this gig is not high enough.
Also "working from my PC" is hell of a thing. "Serious" devs have their setup polished for years. Terminal aliases, utility CLIs, configurations and themes, list goes on.
You'd be better off signing an NDA with the person and suing him in case, of course if the person is legally reachable.