There are several PS rivers that all ready are defacto "gene banks" -

The Samish was last planted in 2006 - winter runs.
Sauk- last planted in 2008 - winter runs
Skagit - last planted in 2013 - winter runs
Deer Creek - hasn't been planted in more than 50 years -summer runs
Pilchuck River - lasted planted in 2008 -winter steelhead
NF Skykomish - lasted planted in 2006 -summer and winters
Tolt - last planted in 2008 -summers and winters
Nisqually -hasn't been planted in over 20 years - winters

I think Chambers Creek hatchery steelhead were last planted in Hood Canal rivers in 2004. However there are a number of wild brood stock programs on those rivers.

Curt