You want me to give away my secret hunting grounds?
Only kidding... I have no secrets.
Honestly, there probably aren't too many places I haven't checked out yet... as far as the usual suspects go. The antique and junk shops are all hit or miss... it just depends on the day, but I rarely find much. The local thrift shops (Salvation Army, Goodwill, and the like) all seem to have people behind the scenes keeping iron from making it to the floor (selling on Ebay perhaps?)... or there is another iron hunter who always gets to it first. I have only found 3 pieces of cast iron total at the thrift shops- a modern Lodge #8, a Lodge guitar novelty piece, and modern made in China "cookie skillet" (I bought it for a spoon rest... it was $1). That is seriously all I have found in the last 6 months.
All that being said, estate sales are becoming my only hope. I have gotten the best deals and the luckiest finds (all covered in gunk hiding their ID and value) from estate sales.
If you plan to pass through Montgomery area (I-65), you may want to give "Prattville Pickers" antique mall a try. There's at least one dealer there with a good amount of iron... some at good prices.