I broke the screw in my RSR float valve and found it was a metric threads, so was able to order replacements on eBay. If you have trouble finding your replacements, and can figure out what size they are, this may be an option for you. I have a tap and die set with a screw gauge so was able to figure out mine were M3x6.
I also broke the screw in my Jebao skimmer which is also a metric thread, but in that case was able to get a suitable replacement from my big box hardware (M6 in this case). It seems like these acrylic screws are most/all metric.