Well, back in 2009 I was trading institutional money so was fortunate in that I could access most of these markets via Newedge. But I think that for a retail trader your comments are probably right, that back then, high commissions and poor platforms were probably the norm for retail clients wanting to access these type of non-mainstream exchanges. Anyhow back to the present … I’ve made contact with all of the recommendations generously provided in this thread, and to date it looks like RJO and Berkeley are the two that appear to have the broadest coverage of those exchanges not available via IB. Still ironing out commission levels as well as platform options, but happy to keep you in the loop as I progress.
I'd be interested in what kind of commission schedule and platform you end up working out with either of those two. I've always heard RJO was high commissions.