Good question, just got a cw9 as well. I ordered just the front sight and it is easy to change. Really only reason I ordered it was because the factory front sight is plastic and can breaks off easily.
Do it yourself in less than five minutes. Snap off the plastic sight with some pliers [place a shop towel or something between the slide and pliers so it doesn't get scratched.] Wipe off any oil residue inside and outside of slide. Insert post in the hole, place some loctite on the screw threads and screw it in. Do not over tighten or you will snap of the screw. Let dry overnight and go shoot it.
I think I purchased the front sight from Kahr for thirty some dollars.