Generic polars could be useless. Your boat needs the first reef at 18 knots, mine needs it in 12. Your boat runs fasted dead downwind, wing and wing, mine is faster gybing off. No real way to "average" those variables into a generic.
I'd also found a great Excel sheet to guesstimate polars for boats that didn't have them. It accommodates questions about sail plan and area (is your normal headsail a 130? 150? 110?) and crew aboard, i.e. can you put 600# on the rail or not?
If you can't find an online tool to generate something useful, then you are left to either looking for polars from "similar" boats (perhaps the molds or the design were borrowed or shared?) or taking lots of sails, with pen and paper or the GPS dropping lots of breadcrumbs, to note how it really goes.
Since polars were originally (AFAIK
) a competitive racing tool, and racing is a money game...Yeah, they often have to be bought, or run off for your boat, at a price.