Warn Sound Capacitor

I suggest the Miflex KPAL series. If those are a bit too spendy, I would suggest sticking with a film and foil type, and staying away from metallized polypropylenes. The construction is much better.

Audio4pass, what Values and quantities do you require, and what is your budget?

You might be chasing your tail a bit, trying to find a cap that will tame your tweeter. Something with a high ESR would work, but it would make more sense to just install an L-pad (in parallel to the tweeter, across the tweeter output of your filter) and use it to pad the tweeter level. Once your tweeter level is comfortable, remove the L-pad and measure its resistance. Purchase a high quality resistor of the same value, and install it in the same location.