You can find people with COBOL knowledge, if you need them and can pay them - or can train them. If you are planning multi-decade projects like major defence procurements are these days, then training people up-front would be worth it.

Incidentally, there are possibly millions of people with daily exposure to a subset of Ada - its the basis of Oracle's PL/SQL. A component of the PL/SQL parser is called DIANA, which true Oracle geeks know is Descriptive Intermediate Attributed Notation for Ada. See http://stackoverflow.com/q/7764656/447514