Oh man, are we on diametrically opposed positions on the tattoo scale. I fucking hate that sacred celtic shit and I'm Irish. I even have some knotwork from almost 20 years ago so I know the allure.
But to each his own.
I'm not sure how experienced you are with tattoos, but you do have a bit of a dilema. Seattle has way too many shitty tattooists. ESPECIALLY shitty tribal/celtic/whatever tattooists. The style requires far more attention to geometric consitency and percision than it does to artistic interpretation and technique (imho, natch).
In short, it's way easier to fake celtic images than it is more traditional american or asian stylings. And the bigger the bullshit about spiritualism etc coming out the mouth of the inker the more likely you'll wind up with a shit tattoo.
But I dig where I think you are coming from. You want something as authentic as possible coming from someone who fucking means it. Good on ya. Just beware. It leaves you ripe for the plucking and you can get ripped off.
Having said that and having just insulted you a wee bit (in fun, I hope you take it) I recommend going to down to Under the Needle to talk to the Joel there that does the tribal stuff. Not the Joel that does the tradional stuff. I don't know that he does celtic but his tribal is very good and the work holds up over time. He would at the very least be able to point you in the right direction.
I'll also ask some inker friends later and see waht they say.
Good luck