How to take a Photoshop brush and vectorize it for Illustrator strokes tutorial, how to convert brushes to vectors
If you have a brush stroke in PS you don't have to keep it solely in Illustrator. You can apply the brush stroke in Photoshop to a layer and then drag the layer into the CC library and then drag the item from the CC library to the artboard in AI. Another way is just to apply the brush stroke to an empty document and export the artwork to PNG or TIFF and then use the place command in AI to bring the stroke.
You can use a single stroke or perhaps create a far more complex stroke with multiple dabs of the paint tool in PS or perhaps add effects into the mix such as poster edge or third party plugins to create distressed or rough strokes etc.
You can find a selection of sets of artworks that may be of use such as face brushes as well as face patterns as well as face strokes for Photoshop etc and if you don't want to manually convert them into vector artworks then fonts are always a great source of designs as well
Once you have the image (however it is imported), you can then use it as an AI brush straight away by dragging it into the brushes panel (with the most recent versions) but if you want to use it is a vector then you can convert it into a vector via image trace.
Select the imported / placeed image and click image trace.
Display the image trace panel and change the treshold as required
expand the artwork.
Create a small nil fill and nil stroke path and use the select menu select similar fill and stroke and delete all the empty paths leaving only the black path.
You can then combine all the paths of the stroke using the pathfinder panel
Select and copy into the brushes panel and save it as a scatter or artistic etc stroke.
You can find our selection of 16,000 Illustrator brushes strokes perhaps of use and they can be combined with any of the strokes from Photoshop (as well as exported to PS)