I use my own from the backyard. The branch should be wider than your dragon, since they are not particularly great climbers. A good solid 2-3 inch wide branch should do fine for quite awhile. My dragon likes laying on her branch and letting her legs hang down 
You just have to clean and sterilize the branch really well. I usually take a stiff bristled brush with soap and water and scrub it down really well. I have to use the tub, since I have done this with branches up to 6 feet long! Then if it fits I put it in the oven at 200 degrees for an hour or so. If it is too big for the oven I use a bleach and water solution, rinse well and then lay it out in the hot sun for an afternoon. Make sure you clean really well....back in my novice days I didn't clean a branch really well and about a week later flying anys hatched in my water dragon cage! Luckily they were attracted to the dragon's pond and most drowned, but still, my mother was less then thrilled LOL 
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A mans got to do what a mans got to do. A woman has to do what he can't.
Mom to:
1 little boy born 7/19/04
2 male RES, born 1999
1 ribbon snake, age unknown
3 FBT, ages unknown
1 female bearded dragon, born 5/2002
1 male lab mix, born 5/24/03
1 female calico cat, born 6/7/04
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sig file edited 1/29/05 [phw]