I've not been there, but I understand Bohnhoff Lumber is one of the biggies. I believe they supply a lot of commercial shops, but they accept walk-in customers.
Did you have any luck with finding Ipe and what was the LF price?
I'll be doing a deck on the first of my outdoor builidngs in the next couple of weeks and was thinking of buying it out in LA if the price is reasonable rather than order it here and have to transport it.