This is a tough one. In my experience these guys don't like to ride shotgun (assist), they want to run the show.
I used to check in with Industrial Coatings & Sealants in Mukilteo prior to doing this kind of work .. they were wickedly helpful in advising on which type of concrete to use (apparently, there are some that lose very little volume when they dry), how to apply acid-reactive stain, also hot-tar-rated epoxy-based sealants, and clear epoxy top coats. They also recommended contractors to advise and sold the requisite tools.
They were purchased by a huge chain a few years ago .. I don't recall the name, so they may not be around anymore. You could try to look them up and see who bought them:
Industrial Coatings & Sealants - Mukilteo, Washington 12521 Evergreen Dr, Mukilteo, WA 98275
That said, if you look for Kemiko dealers in WA State, there's a place call Westside Concrete Associates in Lynwood. I'd call them. Kemiko makes some really great products to treat concrete (like a set of acid-reactive stains), and they require expertise above and beyond "mix concrete and pour", and they're likely to have contractors who are skilled in this area (they definitely have a massive set of concrete products).
Westside Concrete Associates – Lynnwood 412 164th St SW, Lynnwood, WA 98087 425-582-9977
I've also walked into Salmon Bay Sand And Gravel in Ballard and they were pretty helpful. Their product selection is fairly limited. They were annoyed with me because I didn't really know what I was doing, so be prepared to be mocked if you go in and ask questions .. but you'll eventually get what you need.
Thanks Tom. Very helpful. It's clear you know your way around a bucket of cement!
I know what you mean about pros not wanting to work with amateurs. I'm prepared to be mocked (that happens all the time) and to get the cold shoulder... and be relegated to full DIY. Seems that once you figure out the correct materials and do the prep, it's a pretty straight forward project. Here's to hoping I don't have to eat those words someday.