Yeah, regular water lettuce can reach up to 18" in size, but dwarf water lettuce the biggest pieces I had were 3" in size. They're great for soaking up excessive nitrates in aquariums, I had mine in my 45 gallon tank under a cheap LED fixture, and they would reach 1" in size, but under a T5HO light fixture they get 3" and fill the top of my tank every other month then I'm forced to clean them out and give them away every other month!
And check -
http://www.plantedtank.net/forums/
You can ask for some in the California area of their forum, or find people selling them in their for sell area too.