Approach Control Frequencies

Flew to West Virginia yesterday from Lee Airport, nead Annapolis, MD.
Filed an ADIZ flight plan, called Potomac Approach and got a squawk code.
Flew out of the Baltimore-Washington ADIZ with no trouble, but requiring
several frequency changes as I was handed off from one controller to the
next. However, when I returned, I took a different, more southerly route.
Here is a copy of what I sent AOPA describing the events surrounding my
attempt to re-enter the ADIZ:

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Filed to enter the ADIZ at 11:15 local at the Brooke VOR (BRV). Arrive
exactly on time. Called the frequency on the chart for that area: 119.85.
No response. Tried another freq for that area (on the chart): 124.65. No
response. I had decended from 4000' down to 2000' to go under the Class B.
I tried 126.75 (typically for VFR North of this area. No joy. Called
Stafford Reginonal airport nearby. They suggested 120.82, which they told
me was a "new one" they were using. They also reported that I was "loud and
very clear", when I told them the problem.

Several times I heard, "8593V, you are loud and clear. How do you read?".
However, when I responded they didn't hear me. I climbed to 4000', and
tried 124.65 again. This time I got a response and they could hear me. I
got a squawk code and was told to proceed (after being led to beleive that
he could not find my flight plan). He told me that below 1200', I could
have contacted Quantico Approach on 127.05. I asked him how I was supposed
to know that, and he told me that he did not know. How are we supposed to
know the approach frequencies and their limitations, if not on the chart?

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Is there some place we can get the approach control frequencies for a
specific are, ... and their limitation?

TIA

-john