Pairing Icing Flavor with Cookies

How about lemon? I think chocolate goes very well with citric fruit, and instead of flavor you could use real lemon juice. It will also hide the meringue powder taste. Or chocolate flavor. Or use real egg white / dried egg white instead of meringue powder and go without flavor. That's what I usually do, I find that flavoring either the cookies or the icing is enough. Both seems a bit too much to my taste buds

As I don't work with flavors much, I am not entirely sure. But I dimly recall I have seen it somewhere. There is a brand, at least in Europe, that sells clear extracts in about any flavor you can imagine, chocolate should be available. I am pretty sure there will be something equal in the US.

Yes there is chocolate flavor.  I bought it once.      Other flavor could be mint,raspberry or cherry, but the best is to make a  test first to be sure the flavor works. Some flavors do something in your royalicing finish.  

I flavor my cookies and leave my icing as vanilla. This way whatever icing is left can be reused and I don't have to keep track of what flavor it is.

Although flavoring it a smidge does sound yummy

orange also goes really well with any chocolate which i even sometimes forget lol you should try a plain chocolate cookie with orange icing would be yummy also coconut! my favorite cookie in the world is chocolate chip with coconut and pecans so i think if you find a good coconut extract that would be amazing with chocolate chip cookies