There is modelmayhem.com for those who are interested in professional modeling. Some will indicate an interest in tickling. Onemodelplace.com is tougher, since I'm told they don't allow a specific tickling mention.
Someone in the New York (tickleabuse.com), Florida (jw ties), or California (tickling paradise) can find producers and eventually make their way to them, I would think. Renee from tickling paradise has an e-mail list, and jw is on FetLife.
Mistress Xena from Chicago offered me a chance to be in one of her videos, so I'm sure that a girl could approach her since I've seen clips of hers with girls.
FetLife also has a group for producers (of all fetish types). Occasionally I see a casting call for ticklish women out there.
Plenty of opportunity for someone with a legitimate interest.
Thanks for asking.