Oh, and since jsteel mentioned online stores:
www.aquaticisland.com has:
Nassarius Vibex, Cerith, Margaritas, and Red Tipped Hermits for a very low price.
www.reefermadness.us has:
Turbo Snails, 14 Margarita Snails, Cone Trochus Snails, Cerith Snails, Astrea Snails, Scarlet Reef Hermit Crabs, Red Leg Hermit Crabs, Hawaiian Left Handed Hermit Crabs, Nessarious Snail, Tonga Bumble Bee Snails, Mithrax Crab, 3 Tonga Fighting Conch, and Queen Conch in their cleaning pakage; though some are either/or. I have never ordered but it is very diverse.
www.saltwaterfish.com has:
Scarlet Hermit Crab, Blueleg Hermit Crab, Turbo/Astrea Snail, Nassarius Snail, Coral Banded Shrimp, Emerald Crab, Brittle Star, Sally Lightfoot Crab, Peppermint Shrimp, and quite a bit more depending on their package.
www.premiumaquatics.com also has a selction.
In the end, most online saltwater fish stores will have cleaning crews; some good, some 'bad'. It is really up to you. I personally do not want to spend more that a $1 on a snail unless i buy locally.