Online is by far the best way to buy 9x18. Though I've been noticing lately that more and more stores seem to be carrying it, although at higher prices of course. I just bought 500 rds of the Fiocchi pictured above from Dan's Ammo, for use in my FEG SMC-918 (No steel-cased ammo for that baby). I also bought several boxes of the Brown Bear from....Midway, I think, that was less than $5 per box. That's steel-cased (even though it looks like copper), so only goes in the Bulgarian Mak, but it's very good range ammo. And I'm sure I have a couple of boxes of Wolf 9x18 in the bottom of one of my ammo cans, just about every Mak owner I know has some of that stuff laying around.
As for defensive ammo, Hornady XTP's are available in 9x18, although they're loaded lukewarm (965 fps or so, 95 gr. bullet). Cor-bon used to make 9x18, they've dried up but rumor has it they're about to release a 9x18 PowRBall, which would be great. Cor-bon is about the hottest-loaded carry ammo out there, and their old 9x18 was tested to be the best-expanding HP in that caliber.
Then of course there's the Silver Bear JHP's, which are very inexpensive, seem to have good consistent loadings, the bullet machining is a bit crude compared to a Hornady, but they use 112 gr. bullets, which is just about the heaviest 9x18 out there. That's what my Bulgarian gets loaded with on the nightstand. The SMC-918 gets carried with XTP's alternating in the mag with some of my few remaining Cor-Bons. (Bring on the PowRBall!)