Do you have a particular year in question?
Should you go to the H-D website,click on parts & accessories,then Softails,then front end components and then on to forks,you may come up with:
part no 48645-99 GLOSS black lower fork sliders.Fits 08 and later FLSTF and FLSTFB.$300 U.S. Sorry,i know you wanted matte black,but H-D only appear to offer gloss.
If you do decide to buy gloss,just punch in "48645-99 on e bay" to your search engine and have a look.I'd be very surprised if you couldnt get some for $100-$150 cheaper than H-D.