I wouldn't say it is illegal. But yo ugot to be carefule. You will want to make sure they are over 18 years of age which means get a copy of their Drivers License or ID. Make sure you audition them to. Now how to go about getting them. The easiest way I found was to put an ad in the local alternative and college newspapers. Here is the ad I used:
Watend, women from 18 to 35 who are ticklish to make videos. No sex or nudity involved. If interested, call XXX-XXX-XXXX
That got me a ton of calls and 40 auditions. I also have a friend who put the following ad in his local college paper:
Looking for a lady friend who would like to share in a little foot tickling fun. Totally innocent, no sex or nudity. Serious replies only call xxx-xxx-xxxx
He said he got about 25 calls and 5 ladies to have tickling fun with.
Hope this helps. PM me if you got any specific questions.