I’m on the German platform “joyclub.de” which is one of the very well crafted and serious Swinger sites with more than 300K regular Users and good balance of couples, singles, M / F. Not many fake profiles there, good quality management.
There are groups for any special preferences and tastes. The group that unites the big dick lovers is called “Big Dicks and Chicks” and it is about only 6-7% of the total active population of Joyclub who are members of that group (and half of them are males with supposedly big dicks).
That platform is really only about sex (and some BDSM) and people post very explicit pictures of themselves and are pretty open about their preferences, also the more exotic ones, I would say that female profiles mentioning a preference for big dick size is probably also around only 5-10% (my own anecdotal evidence) - therefore confirming the 7-8% figure from the specialized group.
If you go and date online or in a dance club, you go into the most competitive situations, where women have all the selection power.
Any women on sex dating platforms (even those without pics) get dozens of requests every day. So it takes a lot of labour to get their attention.
I have found that picking up women at the tram stop, in the book store, in the library or even in the grocery store is much more fun and NO COMPETITION. Also, it adds the element of surprise to them.
P.S.: Besides that, picking up women in a book store already is a great pre-filter as you can be sure they can read.