I think Black wattle would make a great self bow. There are two problems though; here in Australia we have some like over 900 species of Acacia wattle] and about half a dozen or more known in their respective localities as 'Black Wattle' The 'true' Black wattle is Acacia Melanoxylon. Most gums aren't really suitable for consideration in making self bows, due to high resin counts,and less than desirable qualities in stress and strain tests.With black wattle also, it , at least here, is often riddled with borer holes making getting a suitable length quite hard. Reckon you would find a good bit you're in with a big chance of a successful bow. I know it makes great lams.