Search for companies that need to design sophisticated hardware at very low cost. This pretty much guarantees they need to hack microcontrollers, which are usually programmed in C. One I've worked with in my past life as an embedded developer is TI MSP430 (costs pennies), but there's many others.
Another route to code in C close to the hardware is to find work writing Linux kernel device drivers. Of course, you have to know the Linux kernel fairly well in addition to being a good C programmer to land that sort of job. Companies that need this skill include server manufacturers that design their own network interfaces and such, and perhaps phone manufacturers, or companies that design their own SoC's (Qualcomm, TI, etc). Maybe some IoT startups need this skill as well.
Yet another way to code in C is to work in a place that needs to program DSPs. Usually, this also requires knowledge in video/audio engineering. Companies that need this skill design and sell devices that do some sort of video / audio encoding (like video conferencing devices, etc).
I'm sure there's many others I'm not thinking of. I hope this helps...
Another route to code in C close to the hardware is to find work writing Linux kernel device drivers. Of course, you have to know the Linux kernel fairly well in addition to being a good C programmer to land that sort of job. Companies that need this skill include server manufacturers that design their own network interfaces and such, and perhaps phone manufacturers, or companies that design their own SoC's (Qualcomm, TI, etc). Maybe some IoT startups need this skill as well.
Yet another way to code in C is to work in a place that needs to program DSPs. Usually, this also requires knowledge in video/audio engineering. Companies that need this skill design and sell devices that do some sort of video / audio encoding (like video conferencing devices, etc).
I'm sure there's many others I'm not thinking of. I hope this helps...