For what it's worth, I book reward nights relatively frequently in Portland, but there is almost never availability until the week before. If there's nothing available a few weeks out I usually just call every day starting a week out and have been successful every time I've tried this in the last year or so (maybe 3-4 times total - at the RiverPlace, our first choice, or the Vintage). But it sounds like you're trying to book close-in, so maybe even that approach doesn't work in the July/August high season...