Pascal has two free and open source compilers, GNu Pascal and Free Pascal. So how many does ADA got. And Cobol?
Very few, but there are some: GNU Ada (gnat) & COBOL, GWADA, some DOS and Win32 COBOL compiler called, imaginatively "COBOL for DOS/Windows", and a couple or three more whose names elude me ATM. I know of at least two or three for each of the main platforms: Windows, Linux/BSD, MacOS.
Then there are the almost COBOLs and "quasi-Ada"s out there, but those don't count
Make an experiment, if you're on Linux: open your package manager and search for COBOL/Ada. For example, one of the finds mine yields (not exactly a "compiler" but...):
OpenCOBOL implements substantial part of the COBOL 85 and COBOL 2002 standards, as well as many extensions of the existent compilers.
OpenCOBOL translates COBOL into C and compiles the translated code using GCC.
But the question, really, is not how many free compilers exists but whether the existing compilers, free or otherwise, are generally "standard". And the answer, with COBOL and Ada, is that most, if not all, are. They simply have to be or they wouldn't be used: that's why I said that their standards are the most succesful. Not the language themselves:
the standards.