Bob - if you're up for a little adventure, I think I saw some off a rollerblading trail near Blanchard Park (just east of Rouse road, heading towards University High School). Might need to deal with critters, I suppose. But it would be free and (possibly) fun .
So many responses to filter through. At this point I think I will stick to the Phyllanthus. I have had it in the past and it was an interesting plant. It also fits the biotope and will add a color contrast.