some of the locking buttons are missing from my convertable cover.
(boot??)

where can I find some more to replace them??
I hate it when the front of it pops up into a parachute on the freeway.

 

I don't believe the buttons on the cover itself have a part number but the first place I'd check would be a dealer. If they cannot come up with something, a talented convertible top repair company in your area may have something that can replace it. I do know that the combo bolt/button portion which is on the car itself IS replaceable and depending on which ones are missing there are a variety of part numbers which can be referenced either at a dealer or via the parts microfiche online at mazdaformance.com or elsewhere.