I dunno is the short answer. I'd like to is the longer one. Mike at DC Indexes, which is a terrific site, has a master list of DC Comics. If we just say 1955-1970 is the Silver Age, DC published 5,863 comics. From a friend's list of Marvel Comics I got 1,672 for the 1960s alone.
While there weren't as many publishers as in the Golden Age, there were some substantial publishers--Archie, Dell, ACG, Quality before they sold their titles to DC, Charlton, Harvey, Fawcett. I have a master list of all Harvey Comics which shows 6,753 issues but I don't know how many of them are Silver Age. If we estimate that it's 1/4 of their total, that's another 1,690 comics which would put us over 9,100. Archie would seem likely to have had at least another 1800 or so, which would put us near 11,000. So I'm pretty sure the answer's somewhere north of 12,000.