I looked into smoke grenades a while back and wasn't very happy with anything I found. Hazmat shipping fees are a bitch, and it's really hard to judge a grenade by the amount of smoke it puts out. Weather conditions change smoke performance so much that I'd rather have many smokes than few, regardless of how much smoke they put out.
The best deal I've seen is what Jason_in_Va (aka 556ammo) puts out. He's got the army smoke grenades, but he also has two types of maritime smoke grenades. The only real downside to them is you can only get orange smoke. The upsides are great though. They come in 2 minute and 4 minute burning versions (the 4 minute versions are kinda bulky), there are no sparks (cold burning = less chance of starting a fire in the woods), they're self-igniting (via a pull string), and the best part: they're 10 bucks apiece. I've got 5 of the 4 minute versions sitting in an ammo can at home right now, next to two M-18's.
Not trying to rain on your parade, just presenting an alternative.