You could attach a 1x4 wood strip to the chimney with cut masonry nails into the mortar joints, then screw the bracket into the wood, or you could use a hammer drill to make the holes necessary for some plastic anchors and attach the bracket directly. The masonry nails have no power to hold into the material, but they effectively pin it from side-to-side movement. You would have to determine if such a fixity suits your design. Anchors have side-to-side fixity and withdrawal resistance to boot.
Casey

tapcon screws attach into brick..
use masonary bit smaller than tapcon screw
to drill pilot hole and drill to screw in tapcon screw

just a thought.

I have tapcons....was not sure If I should go into brick or mortar though...

"I have tapcons....was not sure If I should go into brick or mortar though..."

Either is fine sine you do not require an actual rated joint.

Make sure you use the correct size drill bit for Tapcons, a drill at least 1/2 inch or so deeper than the screw will be inserted, and then blow the dust out of the hole.

Oversize holes really weaken tapcons withdrawal strength.