You could try either relaxing the degree requirements, or reaching a wider audience -- I generally don't see firmware jobs advertised on HN and StackOverflow and those are basically the only two places I ever pay attention to job ads. Depending on your existing volume of applicants you might also ask them to attach a semi-trivial C assignment to their application. Yes, this is accessible to anyone who can google, but you might weed out the disengaged who don't care enough to read the instructions that way.
Another dynamic at play is the fact that those who don't have useful skills apply more often as they continue to be out of work, that doubtless accounts for some of it.
Still a bit strange.
Or they've never touched either C or an embedded system in their life, but somehow it ends up on their CV and they tell you about how passionate for learning they are. Which may well be true, but it raises questions about your honesty and/or capacity for introspection. Also, bare-metal embedded really isn't the place to learn C[1], given that most failure modes are "It doesn't work. And maybe something caught just fire."
[1] Ask me how I know...
"Oh I have to stream data into my processing routines with not nearly enough bandwidth? No problem."
I've also had smiles of delight when devs got 100% raw access to every little bit of hardware. Discovering DMA controllers is /fun/ for them. We came super close to getting a decompression routine running completely by our DMA controller!
So, it seems you need to either accept a recent CS grad who seems adept at programming and can learn, or pony up the 200k+/yr to poach someone if you want to hire quickly. Most people I know that have done embedded work tend not to move around a bunch and aren't motivated by small amounts of money to move jobs, so you'd have to offer a large incentive to find the good people.