How to survive as a postdoc with unsupportive mentor and team
I am actually in a situation that's similar to yours in a lot of respects (i.e. at the end of a postdoc and not that much to show for it due to lack of collaboration with my team for various reasons). So I'll give you some advice I have been trying to apply myself - although I haven't quite succeeded spectacularly so take it with a grain of salt.


It's a systemic problem. This is not practical advice on what to do, but emotionally, you need to try and kind of self-distance yourself from this situation to realize that academia does not encourage researchers - after their PhDs and before tenure - to go out on a lim exploring something deep that doesn't show immediate results. There are no mechanisms for consideration of effort and risk and potential impact of success, while an epsilon-improvement on the state of the art in what's fashionable is usually a sure-fire success.
Finding collaborators is job #1. Unless you can churn out award-winning work yourself, you absolutely must find collaborators. Maybe that means quitting the group, eventually. In the mean time, be very very active in contacting people who do work you feel you could build on or collaborate in, introducing yourself, talking about your plans etc. Possibly also out of academia if that's relevant.
Try to bargain with your mentor You're expecting your mentor to behave in certain ways, but s/he isn't doing so. You should have (and possibly still can) talk it out with him, in the sense of realizing why he is acting the way he is
If you can, try to get direct access to students You mentioned trying to work with tenured faculty's students. If you could somehow get in touch with prospective students yourself, that would be a bypass. Proposing to teach a workshop or proper course, or to co-teach something, or to offer a "lab project" course, or to give a guided tour of the lab's activities, could help. Of course, that has a cost in terms of effort.
Take the time/effort to also pick more low-hanging fruit Try to either branch out to a close/related subject, or work on a problem in your main subject of interest, which you think is not very significant - i.e. probably the opposite of your intuition regarding how to choose what to work on. While this would not yield a great publication, it could yield something publishable and opportunities to talk to people and make connections. It would also make it not appear like you're unable to produce anything in the bottom-line sense.
Explore collaborations with your PhD advisor and his/her group. You did well during your Ph.D; I assume the people around you did not all die in a car crash... talk to them, especially your old advisor if you're on good speaking terms. In fact, you could even ask for their advice on your predicament (that's orthogonal to suggesting collaboration).
Explore opportunities for funding. While this requires collaboration with a more well-established academic figure, you should still give it a try. In fact, it might be an opportunity to bypass your own mentor if s/he is not interested in helping, by talking to the more senior / most senior people in the lab. If you manage to secure funding, that would almost be like getting students; it would mean your lab and even your mentor would be more committed to promoting the research you're doing; and it's an important thing to have on your CV.


Note: These suggestions are not comprehensive and are not in any particular order.