If you want mainstream, Ticklehunter is the MAN! He has 100+ vids on youtube which although all /m (Which isn't my or most people's first choice) still contain some of the best clips ever committed to celluloid. Highlights include:
A short advert for French chocolate which involves a guy strapped into stocks by some sexy women who use a goat on his feet, prompting frenzied, bellowing laughter.
A chinese guy in a prison with his feet held up in the air being tickled by what appear to be two prison wardens. Pretty long and drawn out.
The classic Norman Hunter scene where he offers to clean a kid's window, is locked outside with his feet sticking through and then tickled for quite a long time with a feather until he agrees to do something for the kid (Which I think is the best scenario for mainstream tickling, preferably minus the kid obviously).
A scene from a Western in which a gang has a guy captive and begins tickling his bare feet because he's getting lippy with them.
A Spanish speaking clip in which I can't figure out the plot but a woman has a man tied to the bed and tickles him, in again what appears to be an attempt to force him into agreeing to something.
And two of my favourite mainstream scenes of all time - The first is from Western Cyclone, an old Western movie that looks like it dates back to about the 50s. A sheriff has taken an outlaw's boots off to burn them as a means of torture but reveals he can't do it "Even to a renegade". He then tries to light a match for his cigar, fails to, and lights it on the outlaws foot, discovering that he's ticklish. He says my favourite ever line involving tickling - the gloriously simple "Oooooh, Ticklish, eh?" - and then tickles the shit out of him. The clip isn't great quality and the laughter sounds a little bit exaggerated, but the scenario that leads to it is great.
The second clip appears to be from the same film as it has the same actors, and is basically the same except the buildup is different: a guy rides up to a farmhouse and hears someone screaming, draws his gun, and then enters to find that the screaming is coming from the guy in the first clip. This one is slightly higher quality and lasts longer, and the man being tickled gets even more desperate which I personally love to see.
Ticklehunter is the God of mainstream tickling and if that's what you're after then getting on his channel is an absolute must! Hope this helped 🙂