I would say your best bet is going to be independent CFIs, not affiliated with a school, and perhaps even ones that do not have their own airplane to teach in. In other words, like me...
Personal anecdotes follow:
Since I do not have an airplane, all of my teaching is in owner's airplanes. As a result, it's in a wide variety of airplanes, and I get a wide variety of training requests. Virtually none of my training is "let's do turns about a point". Instead, people come to me for exactly the types of things you're talking about - improve existing skills and work on things that are not included in the various checkrides. While I don't specialize in any particular type of training, if someone comes to me with a specific request, I will build a training plan to work on what they want. While this is most often for avionics upgrades, autopilot/GPS training, instrument refresher, etc., I have also done training such as "can I spiral down over a field in IMC, break out at 500 feet and still land?" and "can I land in a 25-knot crosswind?" or "how high do I need to be to make the "impossible turn"?"
There are only a few types of training that a CFI can really specialize in and have a reasonable career at. Upset/recovery/acro is one. Type-specific training (Cirrus, Bonanza, etc.) is another. Specific avionics training is a third. Of course you're not going to find a CFI who specializes in just "engine failure on takeoff" training, that's way too narrow.
If the CFI you've been using for other stuff seems proficient, flexible and willing to prepare lessons outside of a regular flight school curriculum, then try them out. Otherwise I think the suggestions for contacting an upset/recovery/acro CFI are excellent. Maybe even get some spin training while you're there!
