How many US 500 dollar bills were printed in the 1950's?

None. The last high-denomination bills were printed in 1945, although all carried the series date 1934.

No new ones were printed due to low demand in those pre-inflation days. Distribution of existing bills was halted in 1969 in an effort to combat their use by organized crime. There have been occasional calls to print new higher-value bills such as $200 and $500 but it's very unlikely given concerns about money-laundering and terrorism.