While Worldmark has most of the Coast timeshares, any summer week would be an anomaly. WM mostly deposits off season weeks within about 9-10 months. I've never seen a summer week. That doesn't mean it hasn't happened, but it's rare enough that I wouldn't count on it. Booking for WM owners is very competitive and difficult to book so an exchange would be difficult. However, there is a healthy rental market, which makes booking by an owner difficult so that may be an option for you. Put in a request and see what comes up, then try for a private exchange and then rent as a last resort.
Non-WM timeshares are in Newport, Lincoln City, Rockaway Beach, Cape Kiwanda and Cannon Beach. Location wise, the latter 2 are better. There are more at Rockaway Beach so more of a chance to get those, but I don't like the area much. The Embarcadero in Newport is partially timeshares and partially privately owned with quite a few rentals. It's back on the bay and not on the ocean but it's more centrally located if you want to drive up and down the coast.
Sue