The Siletz is known for having at least some Steel in it, every month of the year. But of course, there are peaks to the runs too. Like Chris said, the summers are starting now. June and again in September and October, are the peaks.
BTW. The Siletz and 'Tucca often vie, for the honors of "third best" summer run streams each year. The only streams that outproduce them--which are larger and longer streams--are the Rogue and the N. Umpqua.
If you're interested, I may have maps that I can post.