Haha, You're doing something seriously wrong if you can't find them.
Quick and easy process to find hermit crabs:
Look in rockpools.
Find snailshells(Check under rocks, etc)
If it has legs, you've found a hermit crab.
Pick up hermit crab and put in bucket.
If no legs then poke snailshell.
If it falls over, you've found hermit crab.
Pick up hermit crab and put in bucket.
If it's stuck to the rock, you've found a snail.
Move on.