The syrup is a key for the beer tasting the way it does, rocks/sugar have very poor flavor in comparison. If you don't use it you are on your own for figuring out how to make it taste the way you want.
You can order it online at a whole bunch of stores, its really common. Brewmasters Warehouse is where I got my last order from but I'm pretty sure you can also get it at Northern Brewer, Austin Homebrew Supply and others. I think both of my LHBS carry them now too.