We just started adding western dressage to some of the local schooling shows here (Southeast) a couple of years ago.
You certainly wouldn’t need (or even want!) a silver-mounted show saddle to show in western dressage here. The less bling the better, for clothes as well as tack. I don’t know what goes in other regions, though. But our western dressage riders don’t dress or tack up like the western riders in local open shows.
The USEF now has western dressage tests.
Have you checked the Western Dressage Association of America to see if they have a chapter in your area?
http://westerndressageassociation.org/
I read in some magazine recently (Horse Illustrated?) that western dressage isn’t going to try to just copy traditional dressage but add some movements specific to western-trained horses. Sounds interesting to me.