These folks have some nice looking patterns...have not tried them myself. I'm considering taking the plunge and trying to learn to "make my own" molds. The ready made ones are $$$$$. If you search on ebay for "stepping stones molds" you will also find a bunch. Best of luck!

Here is a link that might be useful: concrete molds

I just found this. Is it more like what you had in mind?

Here is a link that might be useful: Cobblestone molds

Try Lowe's or Home Depot. Both sell them in my area but look in "concrete" section or building supply.

Go to Hypertufa forum, learn to make your own... I am. You can buy say, 5 cobblestones, press them into damp sand to form an impression, and fill with concrete. Paint, stain, or pigment; your options are only limited by your imagination. I run around on garbage day and take the drawers out of dressers that are being thrown away to put the sand in. You might try the yellowpages for a concrete company - one down the road sells all kinds of stamps, and I can actually view the quality.

Good Luck!