oak wood chips
We used oak wood chips for our play area of swings and slide. Where can we get some oak wood chips?
Marion County Oregon wood products
I do believe you're in luck. I know of 2 sawmills in Oregon that are specifically focused on sawing Oregon white oak and I think both are relatively close to you. You can contact them to see if they have chips available:
Zena Forest Products (Rickreall) - http://www.zenaforest.com/
Monroe Oak (Sheridan) - http://www.orforestdirectory.com/company/monroe-oak-inc
Another possibility might be Oregon Barrelworks in McMinnville - http://www.oregonbarrelworks.com/ However, I think their residues are more likely to be shavings and sawdust rather than chips.