I purchased 4mm and 6mm okume at "Hardwood Lumber Company" (just off I-35 and Northwest Highway). As I recall, their prices were in the range of $24 to $28 per 4' x 8' sheet. For an extra $11, they ripped a couple of the sheets into 11" x 8' strips.

It's not the "official" 1088 stuff, but it is marine grade okume, has very nice grain and surfaces and I've gotten nothing but compliments on my recently finished Chesapeake 17.