proxies in scrapebox all banned

hi
so i have been told on this forum to use public proxies for scraping. When I try to test the proxies that scrapebox provides, all proxies are dead for google scraping. I tried all 8 sources. I got 4 working google proxies, but by the time the testing was done, those 4 were also dead.
My time out settings is kind of low - 8 seconds. could this be the problem? If I increase this, will I get working proxies?
if not, then where am i supposed to get public proxies?