Wow, plastic parts on a brake other than a handle? If it has plastic parts it is really cheap. I rode a Nishiki Pro by American Eagle decades ago and it was a pretty good bike with decent components, Yours is made by West Coast Cycles who bought out the brand name. If you are at all handy, brake replacement is pretty simple and there are lots of YouTube videos on how to do it. There are inexpensive all-metal brake sets on eBay or Amazon. If you need help identifying which brake to use, here is a source at Park Tool on how to identify and repair brakes
https://www.parktool.com/en-us/blog/...identification. If you stripped the threads in plastic, chances are you will need to replace the entire brake rather than get another screw. I wouldn't replace it with one like the original.