You need to buy a .40 or .357 then convert to 9mm. I have a Gen 3 Glock 35 and a Gen 4 Glock 22 and have Lone Wolf barrels in 9mm and 357. I've actually used the 40 mags to fire 9mm and it works fine, but have aquired some 9mm mags as well. The nice thing too about the 9 barrel in the 40 is that it has a larger bearing surface and locks up and shoots better. I let a young man who was thinking about a Glock to compete with, shoot my 35 with the 9mm barrel in it last night and his shots touched each other at 25 yards when he tried it to see where it shot for his sight picture. You can use the standard recoil spring also and it will work well as long as you use full power loads. My Gen 3 I had to go 2 pounds lighter with my 9mm handloads but the Gen 4 works fine with the standard spring so far.
Glock Lone Wolf 9mm conversion with 40 cal mags - YouTube