This is the cross-linking idea raised by Kristin Yu: don't just search for a technique — find who trained where it's taught, and see who nearby (or online) carries that same teaching.
Trainees enrol the same way as consultants: career stage, interests and growth areas feed directly into mentor matching.
A lighter ask than taking on a mentee: "can you read this," "do you have advice on this," a quick methods or stats question. One conversation, not an ongoing commitment — for beginning doctors and fellows starting a research project.