Stephen,
Check out the model railroad section of your hobby shop. There are all kinds of things that are used for scenery. You could even go so far as to buy a tree kit and take the individual branches off it. HO guage is 1/87 scale. That should be close enough for a tree branch. They also have different kind of foliage "clumps". Woodland Scenics is one of the big makers of that kind of stuff. They even have some booklets out on how to do different things.
Good luck.
Bill
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DML M4A2 Red Army
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-- There is a fine line between "hobby" and "mental illness". (Author unknown)