You're going to want to stick to hardwoods for aquarium use.
Your best bet for finding something like this is to look for manzanita bunches meant for decorative uses as they specifically harvest for finely branched pieces. Small sections can then be taken from the bunch and selectively trimmed to get pieces that work for you. Rough areas left from pruning extraneous side branches can be sanded down for a smoother finish.
Quite a few folks who sell manzanita on-line can accommodate nano orders if you let them know what you're looking for even if they don't commonly *show* such pieces on their sites.