Hi, I'm going to model the autumn a little southwest of you. I plane to have mostly green trees with the yellows and oranges scattered throughout, just like the photos posted above. Today I found a great place to get my fall trees. I went to JoAnn Fabric and craft shops. They have the fall follage 80%,70%, and 50% off. I got these bushes with tiny beads (leaves) of red and orange, and various shades of green. You can take one bush (regulary $5.00, now $1.00), and cut off the individual clumps into 5 separate trees. They look like aspens to me, and are very similar to the golden tree peeking over the covered bridge. The trees I made are about 5 inches tall and would look good from HO guage all the way up to G guage.
I (over)spent to the tune of $32.00 but I will get about 30 of those trees, and about 10 trees with the big round canopy like apple trees, plus another 10 that will be scrawny trees to mix into a stand of trees.
The leftover stems that I did'nt use will produce trunks for pines maybe 6 or 7 inches tall (probably 50 of them).
If you don't have a JoAnns store near you, try any arts and craft place (especially a big chain).