Shaving brush is pretty tough, there's also some species of caulpera that would be good, shouldn't be too hard to find on eBay and other online sellers. Check out KP Aquatics, they usually have all sorts of macros for sale that come from the keys.
If you want macroalgae but aren't super stingy about it being green , dragon's breath is a good option and looks amazing, just don't be like me and try to keep it with hermit crabs and an emerald crab. I almost ended up with dragon's breath salad before I ended up taking it away from them