Try a Craft Store
You might find your local craft store carries a decent selection of shells. Unfortunately, the vast majority of shells you find this way may not be suitable for hermit crabs, but there often are some great shells, often in a larger range of sizes. You may have to buy a bag or collection of shells to get one or two appropriate hermit crab hells, but in my experience, a whole bag of shells is usually not much more expensive than a shell or two from the pet store. Look for shells that are in good condition with no cracks or holes. Crabs seem to like shells with nice smooth insides, and the opening should be rounded or D-shaped (very wide or narrow openings don't usually work). Choosing Hermit Crab Shells has more information they types of shells favored by different kinds of crabs.
I have a pretty big collection of sea shells now because I've purchased several bags of shells like this, but I have found some great shells this way. Most recently I found the big beautiful shells featured in the photo on the right.
Treating the Shells
As with shells bought from other sources, you'll want to clean and sterilize the shells from a craft store. Before giving your hermit crabs your newly purchased shell selections, boil the shells for 5 minutes, drain them and let them cool thoroughly. As well, I periodically boil all the empty shells from my crab's tank to make sure they are clean and inviting.
Picking the Right Shells for Your Hermit Crab
See Choosing Hermit Crab Shells for more detail on choosing shells.

