My classmates refer to me as "the pathology interest group"
I've organized clubs and events that have nothing to do with career and academics and if I decided to start a path group, I know at least a couple members of our faculty who would be very supportive. If I could include them as part of my roster, then I might even be eligible for funding. The feeling I get, however, is that the pathology faculty here are laid back and student-friendly, so it is much easier to meet with them one on one than to make a big deal out of my interest.
At least once a month, the hand surgery interest group or the dermatology interest group hosts a dinner discussion on how, for the sake of matching at such-and-such hospital, it is essential to honor every single class and to procure letters of recommendation from the author of their textbook, while contributing significantly to a paper that is subsequently published in Nature. I used to enjoy those meetings until they stopped ordering Thai. I will not subject myself to that sort of stress for pizza or cold cuts and I do not wish to subject anyone else to that brand of nonsense by means of starting an interest group... although, I have the feeling a group of pathologists would be somewhat less cut-throat.
Serious answer: not sure there has ever been an interest group here. We match one or two percent of our graduates into pathology and usually, the physician has both an MD and a PhD. I have some MD candidate classmates who are interested in path, but I seem to be the one who is serious. I could have a change of heart, but I want to be certain because residency and fellowship is a long road (as opposed to the three year residency my college roommate needs to complete before earning his autonomy and fine compensation in another specialty). I would rather delay graduation a year than be uncertain about embarking on this career path (get it? ha ha) so I'm opting for the PSF. The PSF is another option, but no longer one that is popular because you cannot count your year of service toward residency requirements (but you can apply all over the place and have an option of which program you attend).
The pathologists I have spoken with at my school and at other programs are extremely suppportive of my interest. It would take some effort to organize an interest group and I am not sure that having a group would do much for you in the long run. Then again, people say that about me and the PSF, but I like being able to pick the program where I train for a year, without having to complete another three if it does not work out. I have a feeling it will. No matter what, make yourself visible to the faculty, as you have intended. Good luck!