I wasn't given the name of the place, just that it's located at 42nd & Olympic in Springfield Oregon. Using Google Street View, it looks like all there is is a heating/oil company there called Marshalls. I know feather rock is used for certain heating purposes, in a similar manner to charcoal, but it doesn't look like the kind of place that carries/sells rock (from the street view anyway). I'm only a few miles away, so I'm going to drive out and see if I can figure out for certain which place it is later today, as well as get pricing and a few test pieces.
Sources on the web say that Home Depot and Lowes both carry it as well, but I haven't looked into either location. I imagine it would be more expensive from either of those stores than through a more direct supplier, if they even carry it. It seems that every time people say to get a part for this or a part for that at either location, my local store doesn't carry it.
From what I've read, people claim the algae growth does soften the sharp edges, but I wouldn't trust that as the only method of smoothing them out. The cautions I've seen are for more than just the fragments, but I'm willing to put in whatever time it takes to smooth them out, sculpt them, "glue" them together, and pre soak them, if it means I'm able to create a low cost, highly customized rock structure for my cichlids. Right now my cichlid tank is just kind of thrown together, with resin Petsmart decor & red lava rocks. While it's functional, my cichlids are outgrowing the holes & caves, and it just doesn't look at all natural (though the massive fuzz algae growing on both the real & fake rock surfaces is actually rather pretty, and balances the colors out)
I'll post more info when I have it to post.