The Green and Barren rivers are just a short (slightly > 1hr) drive due North into KY; both have very good muskie populations. Even smaller tributary streams to these can have surprisingly large fish in their lower reaches, and do not generally get heavy fishing pressure.
In Tennessee, many of the streams on the Cumberland Plateau have good populations; Melton Hill Reservoir over near Oak Ridge (~2.5-3hr from Nashville) is the centerpiece of TWRA's muskie program and receives the bulk of stocking efforts. It's a very riverine-like reservoir, and fishes well during the late fall, winter, and early spring.