IMHO. Singular IT Human Resources are a valid Single Point of Failure issue.
There are a number of ways to handle this including: safe deposit boxes, firesafes, etc. Unfortunately the majority of solutions require a second person have access to the information (though indirectly).
My best suggestion would be a dual lock kind of situation where no other single person can get them. I.e.: A firesafe with dual locks, a safe deposit box that requires signatures from two different people, etc.
The answer to this question really requires a Threat & Risk Assessment all its own.