anyone can recommend me on a site where I can buy used bike in SF or San Jose?
try seeking websites for the various shops, they take trade-ins, and so there is those options..
where can i find a partner to such a ride? forums etc.
on popular routes, like that, there will be a natural Flow of other riders on the same route.
so you and someone else will already be there ,
maybe being a day apart or meeting up at popular stops .
agreeing on a common pace is the question to sort out.
Here there are Hundreds of riders on the Oregon Coast..
Just today The LBS got 6 bikes sent ahead for the riders
to have ready to ride when they get here.