Just to add some possibilities to your list. Sedum also makes good tree armatures. Once the flower dies in the fall they can be cut off and dried. Some folks leave them until the flowers fall off, others leave the flowers on. They can give you quite a tall tree. I planted a few several years ago and haven't come close to using all the armatures they have produced.
If you have a neighbor with these they may not have cut them off yet, so ask around. They do need to be cut off annually.
Good luck,
Richard
Since moving to TN from GA, I moved my Nandina bushes with me. They make superb tree armatures, after the red berries fall off. You just have to remove the tiny ends that look like bulbs, then you're good to go. I've used them naturally and have painted a few of the trunks a light grey to mimic ash trees. I really love all your (every post) posts in this section and it has given me more insight into making trees than any other post I've encountered on the inter-web. Continue your good work and keep us posted.
HO and Lionel 027
Nandina grows kind of wild around here though it is usually pretty scraggly. I never thought of trying it for tree armatures. I am going to have to do some looking around to see what I have and experiment with it.
Huntington Junction - Freelance based on the B&O and C&O in coal country before the merger... doing it my way. Now working on phase 3. - Walt
For photos and more: http://www.wkhobbies.com/model-railroad/