I don’t know free brushes for those you would have to pay now, beside of the very few bundles where someone gave away the first 3, 5 or 10 bundles for free, before the bundle has to be bought, but these were never free in that sense, that was only a giveaway action for a few early birds.
So, if you can name the bundles you are looking for, I’m sure to be able to point you to most of them, for instance the free Memileo brushes, just follow the link to Pling.com and get them for free:
Memileo Impasto Brushes
But the most resources for Krita can be obtained for free from the outset, and those that you have to pay for now were paid before. There is only one exception for a resource that is no bundle, if you can name it, I’ll send it to you, but clearly name it as the resource that you mean.
Here you can find everything listed in the forum. You always have to scroll down till the site hits the bottom, this will load more bundles that you can download till it says that there are no more bundles to download.
Michelist