I am wondering whether anyone here knows what I can get to enable me to tune into radio frequencies above 115 Mhz. All the radios I have go up to about here, and I want to try to pick up ATC frequencies from local airports (specifically EWR), but I can't find any type of stream on the web for them. I tried searching for such devices but I'm not having much luck.

Try Sporty's pilot shop (here) for starters - you can buy receivers & transceivers with audio-out ports to listen to on your PC. Alternatively, SOME ATC centers/towers provide Internet feeds, but they're very rarely published and always slightly delayed...