Home Depot or Lowes.....will have your "Mexican Black Smooth Rock " available in different sizes. Or you can go to a material yard and get all different types of landscape rock and aggregate. Where are you located?
(What City in IL?)
+1 Lowes or Home depot.
Make sure that all pebbles are too big to fit into a tortoises mouth...If you are using them to beautify a tortoise enclosure.
Out in the garden department, Home depot has the pebbles and rocks on a shelf so that you can see the size before buying a whole bag.
Can't see the image either, but I'll make assumptions. Between my RES and my Redfoot, I've used....
- Aquarium rocks from general pet stores ($$)
- River rocks from Lowes ($)
- Decorative pebbles from art stores ($$$) Make sure to cleanse them of chemicals first!
- Smooth river rocks for decorative purposes from Ikea stores (perhaps the rocks are swedish? eh). Pretty cheap too ($)
You best bet for the money and accessibility is to buy a selection of river rocks from Lowes/Home Depot.