Well, I can tell you that my most recent offering, VILLAINS VIGILANTES AND VELLICATORS, has a whole lot of that! See the link in my signature.
You'll find that most of my stories tend to focus on feet. It's my favorite tickle target! I try to vary my stories and include upper body stuff too, but feet definitely get the lion's share!
Honestly there is gratuitous amounts of foot tickling in nearly if not all of our publications. This however is not by design. It just happens that almost every author and artist we have seems to have a fondness for foot tickling and that preference comes out in their creations. Still the authors also make sure that upper body fans are not neglected and you will often find a variety of tickling locations in each story.
Here are a few suggestions that spring to my mind. Please keep in mind that this is in no way a definitive list. As I said earlier you really should not be disappointed with the percentage of foot tickling you find in any of our current publications. As Xodlirv stated almost anything that he has written the lion’s share will be devoted to foot tickling. The same holds true for most if not all of our authors.