I went through a phase of chasing commons. First with bait, then with jigs, finally with flies. It’s been years, long before I moved to Oregon, so I don’t have any Oregon spots, but I can tell you what I consider an important aspect of chasing big ones.
Find lakes with clear water and low densities of individuals. When you find common carp in clear water and at low densities, you find big ones. Not sure why.
All of my big ones (over thirty) came from spots with clean water and very few individual carp. Town Lake (now Ladybird) in Austin, TX is spring-fed and cold. They get 40’s pounders there. There are giants in Lake Erie.
If I were looking for a giant carp, I would look for clean, clear, cold waters with a few carp. Sometimes the waters not even known to have them have a few, and they are inevitably gigantic. You might consider feeding them on a schedule. Not chumming, if you aren’t fishing you aren’t chumming. You’re just trying to get them to reveal themselves. You can always file away intelligence for use at a later date.
For some reason I bet the Metolius arm at Billy Chinook might be a place to look. Maybe not, just a hunch.
SS