thanks for all the leads! I thought I would share this:
I went to a garden store, sure enough they have pebbles but not the deep colors I am looking for. the friendly salesperson pointed to a rock hounding place across the street. i went there and the owner said they don't sell pebbles but there's a stone company a few miles up the highway.
so i went to that place, it's called "stone center of carolina", and boy, they have a huge collection of all kinds of stones. and I found what I am looking for, it's call the "Mexican beach pebbles", at 40 cents/pound. nice and round in deep grey color (they are not coated). there are sizes from 1 to 5 inches, some with nice dark red patterns. makes me feel like a kid in the candy shop. i must be their first customer to buy stones to put in a fish tank, as the guy who took me to the pebbles was quite surprised to hear it. i guess all their other customers are builders or home owners to build things with stones.
anyways my hunt for pebbles ended up perfectly, and I can't wait to put those beautiful pebbles in the tank! thanks again for helping!