http://customshop.seymourduncan.com/humbucker-under-p90-soapbar/
I'm pretty sure DiMarzio and a few other companies make them also
DiMarzio has a nice selection of P90 looking humbuckers
Rio Grande has a bunch in both Dog ear or Soap bar form factors. I have a Baby BBQ mini bucker in my junior style PRS SE.
How do you like the BabyBBQ? Is it as beefy as Rio says? Tight feel or loose?
And how do you attach that mounting ring to the guitar?
I have a full size TX/BBQ set in a McNaught and I like them a lot. Some have said they found 'em mushy in certain guitars but in this one they're just right, firm enough without being at all stiff. I think David's unique "set-through" construction probably has something to do with that - it's a superlong tenon that extends underneath the maple cap almost as far as the bridge. Brilliant design - gives a touch of neck-through rigidity while still allowing the neck to come alive at volume.
I like it, pretty sure it's a little lower output than the full size BBQ, but it works well for me. I wouldn't call it too tight, definitely feels similar enough to all my A2 based pickups for me to be happy. I've gone back to the Lollars in my Kauer Banshee, but it sounded great in there too.
One of these plates
https://www.stewmac.com/parts-and-ha...0aAqNGEALw_wcB
And one of these rings
https://www.stewmac.com/parts-and-ha...waAq_ZEALw_wcB
firebird and mini-humbuckers fit in a p90 rout too