Hi jeanp! Ballroomdancing isn't *very* popular in Holland, so the only places where you can dance are local studios (either for lessons or dance evenings). But, dance evenings are usually closed events, so that won't help you much

(At least, in my experience...) When they ARE open, you usually need to know somebody at the studio to introduce you.
There are currently 43 danceschools in and around Amsterdam, from Ballet to Salsa. If you know where you will be residing, I can give you addresses to Ballroom studios in the area for you to check out. Maybe they do have an open dance evening, who knows 
"Carpe diem, quam minimum credula postero." - Horace