I got a targeted 3x miles offer on my AA Visa for (among other categories) electronics stores for October through December. Are there other cards doing bonuses for electronic stores this quarter?

It was probably an overall electronics stores purchase bonus, rather than one specifically for Best Buy, that was around last year.

An electronics store bonus should work not only at Best Buy, but also at the Apple Store and other computer stores. (But you'd have to check on the specific terms of the bonus to see if it works online, in brick and mortar, or both. If only in brick and mortar, obviously you can't stack it with an online shopping mall.)