I've gone to Lowe's in Orange County NY, Bergen County NJ and some in the city. They all have had them.
Yes, 3/4" true union ball valves. Those are the ones I use on 90% of installs for the return line. I've also purchased 1", but don't need them nearly as frequently as the 3/4".
BTW, you might not find any in the stores because it seems Alfie has been hoarding them