They stopped making them a few years ago. The bars for the tintops are quite common on eBay but the soft top version is pretty rare. I bought mine NOS from a dealer. I don't think that they were offered in the US even though they were made there.

That would explain why I have never seen them over here.  Now I need to start watching ebay...

i have one on my 4 door and haven't noticed a difference in milage. i got the extension for the middle to make it bigger as well. mine is now moved back andother 5". money well spent i think.