They'll periodically come fly in the ultra high sectors I work at ZME, I worked a pair of them just a couple of weeks ago. They're really never on any predictable route, except when they fly some of the IR routes up in ZKC.
I think the information I contributed to the database here has the current UHF frequencies for Memphis Center. We don't work much military traffic that uses UHF in my area at ZME, so I don't have those frequencies committed to memory.
ZME sectors would be Elvis 33 UH (I work this one), Walnut Ridge (ARG) 35 UH (in the area next to me) and ZKC Blues UH 90. I can't recall what the UH sector to the west of Blues is, as it is well beyond my airspace.