I agree with dude, wupper, and M-W. On the rare occasions it's necessary, I would pronounce 'buoy' as 'boo-ee.'
I've definitely never heard anyone pronounce it 'byoo-ee' as in Buick, including in California. It's true that the Y sound in words with long U is generally less common in AE: dew, due, duplicate, new, news, neutral, tumor, tumult etc. are often /oo/, though I personally say /yoo/. (However, sometimes it's the other way around; I've never understood why so many Britons seem to have trouble pronouncing Houston, as in Whitney or Texas, since it's the same sound as Hugh/hew/hue, but a lot seem to want to say who.)
For the verb 'to buoy,' something closer to 'boy' might be more thinkable, but not for the noun, to my ears; I always assumed those puns about the gulls and the buoys were just not very good puns.
If you like this one, you should also like 'Bowie knife,' which in my region at least is also 'boo-ee.' I bet the guys on the military forum would enjoy helping you with that one too, if you refrain from calling them 'thickie squaddies,' which may just sound to them like nonsense baby talk. (-: