You should be able to find ipe...check the lumber yards and those that supply decking n flooring lumber...ipe would be my first choice...also look for massaranduba,jatoba as well...both work well with bamboo,and ya should be able to find it ...there is also some other exotic tropic woods imported woods as well but those are the more common and easier ones to find ....and once ya find some come back n ask questions about it,and post pics of what you got so you can be assisted in how best to use it...and don't try but DO pick good clean grained wood...do some researching in how to choose proper grain in lumber stock ...
Don't know why ya can't order osage slats from a reputable guy who has already chosen the stock and knows what to look for and what works and what doesn't...