Why hard to find transition training?
I can only speak for a few, not all, CFI's who used to but no longer give transition training, for the reason they dropped out: it's all about insurance.
Insurance company to new builder: "We won't insure you (for any reasonable rate) unless you have transition training."
Insurance company to CFI's offering transition training, for hire: "Your normal policy doesn't cover instructional activities. We'll gladly sell you an additional policy that does, for a few thousand dollars more." For the low-volume CFIs this is a money-losing proposition.