Hey all,
To coincide with the release of robotpy-cscore 2019.0.1 (which includes a fix for FPS stream limiting), I have created packages for some distros that have a python3-opencv package, namely Fedora 29, Ubuntu 18.04 and 18.10, and openSUSE Leap 15.
You can grab them here: https://software.opensuse.org/download.html?project=home%3Aauscompgeek%3Arobotpy&package=python3-cscore
I recommend installing by adding the repository, as it will also pull in a python3-networktables dependency which I have packaged.