I found the people at Caribbean Sea Sports, on the grounds of the
Marriott Curacao, quite easy to deal with last year.  They have nitrox
in addition to air.  The shore diving off the beach is quite good from
there.  (On the other hand, those were the only beach dives I did while
there, so I've no way to compare to other sites.)  Their rental gear
looked like--well, rental gear, but I only needed tanks.  Nobody using
the rental gear complained on the boat dives, though, and none of it
failed in service that I saw over five or so boat trips with another
5-10 people each, most of who rented gear.

John Eells