The Westport Seafood Feast is reknown for showcasing Pacific seafood.
Regions of Puget Sound produce tremendous volumes of Manila clams (Venerupus philipinarium) and are a big hit at the table for their bite sized and very tasty steamers. Am I right assuming you were eating these at the time? (2 inch shells with purple edges internally and brownish markings that appear like mountain peaks externally)
I once grew Manila clams commercially, and have eaten countless amounts, but never found a single pearl. If that's the case, then you've found something rare, but not necessarily valuable.
Sadly though, cooking destroys the structure of any pearl.
It's a nice keepsake from a lucky event.