If you have the ability to get to the beaches across Cholla bay you can find a variety of shells.
We take our beach cars and quads around the backside of the estuaries and golf course. Get around the golf course and get back to the beach but aside from that wait for the tide to go out in cholla and cruise the flats.
The beaches closer to PP and Sandy beach are to hard on shells to find many intact, and so many people normally combing Sandy beach area that if something good pops up there is someone already picking it up. Lol.
Good luck.