Most of the remodel businesses will either be able to do it or recommend somebody...and most of those are general contractor owned.
It can be more complicated then it seems as fireplaces are rarely level and you can't just stick stone against some walls and fireboxes...or you can but it will cost you alot more later to fix it. Pick wisely.
When opportunity knocks it's wearing overalls and looks like work.
A general contractor who can recommend a good mason. I'm sure there are also reputable small home remodeling type businesses you could call, too...Be sure they have a state license if required in your state, you can check their business practices that way.
Also, just like in the horse world, ask for references, AND CALL THEM...like at least five of them....Ask me how I know this...By checking on someone in one of these trades a few years ago, by call #3, I knew he had lots of problems with time management (and drinking).... Great quality work, if A) You didn't mind waiting, like, over a year, for a 6-8 week job, and B) If making zillions of calls about no-shows, etc., didn't bother you...