You are might be a little late to the party, depending on your current fitness.
See the SIR website:
https://www.seattlerando.org/
You'll need to be both an RUSA and SIR member to ride brevets. You'll notice that SIR starts its season, as it seems to one unused to randonneuring, absurdly early considering the local weather.
The brevet calendar is here:
https://www.seattlerando.org/content...club_id=928629
There's also a Winter Training Series, which is really a good idea to ride next year: Those rides start the first Saturday in January and every succeeding Saturday for 9 weeks.
WTS routes for 2020 are here:
https://ridewithgps.com/organization...?tag_names=WTS
You could do those routes whenever..
One should bear in mind that on that really rainy PBP several years ago, all SIR riders who entered also finished. The idea is to get everyone fit enough to do the big summer rides and to do that, we have to start early in the year.
I found brevet riding to be very interesting. I think that's the big difference between randoneurring and general road riding.