I know of places but they are kind of like fishing holes, not many will likely share their "honey hole" with someone they do not know. Where in Oregon are you looking it is a large state? I know of one here in Baker City but it is private yard and would take setting up an appointment with them and having me or someone they know take you there. Do you sell the pictures or is it a hobby? Are you involved in the hobby or just enjoy the old car pictures? L & L Classics in southern Idaho is a huge working yard full of vintage cars. Maybe there is a way you could offer them a bit of cash to take pics or they may let you just take pictures. There are not many left that I know of that still have many old cars. There are a few used as erosion control here in the Powder River
I live in Coburg in the Willamette Valley. I am involved in the hobby I work at a restoration shop part time and am restoring two cars at the moment a 1951 Desoto and a 1954 Plymouth. I just like taking pictures as a hobby not for sale and I don't want to be in anyones hair I just have always liked seeing the old cars covered in moss. My 51 I bought was covered in moss with a siezed motor and hadn't run in 40 years and now all it needs is a break job to be going down the road.