Here's a website listing the shoots South of us.
http://wamuzzleloaders.org/RENDEZVOUS%20SCHEDULE.htm
I usually go to 5 of them in Washington, my favourite is Evergreen, just SE of Olypmpia , campsites with water and power $10/night. Really good shoot also, they have a different trail for the Spring and Fall shoot, plus an 8 station trap shoot with dbles, so you need a SXS shotgun for that.
I carry a letter from the BATF, with the description of "prescribed antiques", a copy of Washington State firearm laws,my PAL,my ATT, and green card, in an accordion file. I only bring muzzleloaders, pistol included.
Ocasionaly I'm asked for my form 6, at this point I'll casually mention, that in Washington you don't need an FFL to buy a muzzleloader, it sinks in then, these are not firearms.
I personally know a few people who have been turned back, because they weren't prepared.
I would suggest you get your green card at your nearest Customs office. Lately they have refused to issue at the border, because of lack of serial #s and their ability to identify.
Cheers nessy.