My heart goes to you both, I work for At&t and I get those requests a lot, things are so tight with FCC regulations we are very limited in what we can say. I can tell you for sure from a customer service stand point we cannot see content at all, just dates and times...cause I've had people beg me on the phone for it. I don't know honestly what it takes to get that information because I've rarely seen anyone get it. But legally, we do have to store that information, its just that no one seems to know how to obtain it.
As far as where it is, our systems that house your voicemails, texts, etc are based on your location, its easy for us to see which HLR houses your info depending on where you live. If you're in Orlando there is one or two servers that would have it, but combing through it all to get it, I have no idea how that all works. Our technical support can narrow down the tower you were on when something was send/when a call was made if it was within about the last 30 days. But I know that doesn't help you in getting content.
My best advice would be to not only have your attorney subpoena the records but law enforcement too, hopefully the double hit will get someone who has access moving on it.
Something else we have in the Southeast part of the US is an intensive care group, specifically based at my call center. They specialize in doing the impossible and figuring out what no one else seems to be able to do. If a representative you ask doesn't know about our ICU group ask them if their manager does. If you file a case with them they get on it right away and see what they can do. If you've both already gone through the right department/compliance center and have gotten nothing it cannot hurt to try them, worst they can say is they can't help.