Hi and welcome! There is a group of people trying to get together in the Portland Oregon area. Try this link:
http://yorkie.meetup.com/cities/us/or/portland/
All you really need to do is find a park with an off leash area that you can reserve, or perhaps a doggy day care would let you borrow their facility for a couple of hours on a weekend. Where there is a will, there is a way. If all else fails, just meet up at a local on-leash park or a dog friendly mall.
You can also post in the Northwest Region forum. Someone there might know of a group already established.