This question is dear to my heart, having been a pre-popularity adopter of a few language ecosystems that did and didn't become popular (including C++, Java, and Scheme/Racket).
You can search job listings on LinkedIn, Angel.co, etc.
But if it's only a small number of search hits, also consider the possibility that even some of those might not be genuine opportunities, so you have to look at each one. Examples of why:
* A hiring manager/lead is an enthusiast of the fringe tech., and the kinds of people it attracts, but not actually using it. Or not an enthusiast, but has heard it's a way to get the attention of some of the best developers. (I have done this, and been clear about it.)
* Startup (maybe more likely to choose fringe tech because the tech cofounder happens to know/like it) that is trying to look like they're doing well enough to be in a position to hire, when they're not yet.
* Recruiters trying to keep the funnel full, so candidates ready as soon as openings available.
* Mandated postings, when the org already knows it wants to hire or promote a particular person, so that person's resume gets turned into an overly-specific job post.
* (I've not confirmed this one in the wild, but it's similar to other growth hacking, and you could see how it might appeal in a market heavy with resume-driven development.) Promoting some tool or platform by faking job posts for it.
Note that this doesn't mean the fringe platform is without merit, and sometimes the merit is self-defeating. The norm in one fringe ecosystem I was involved with, on the rare occasion an established company used it, was for one super-productive person to quietly do a team's worth of work, and... the org never really needed to hire more. (And if that established company got refocused on faster growth, then an MBA is probably going to think they need to switch to a more popular platform, so that they can hire a large number of people "who can hit the ground running", fast.)
Maybe also relevant: consider the risks of investing career in a fringe ecosystem, which was the topic of my first Ask HN post (from an engineering lead ethical perspective): https://news.ycombinator.com/item?id=23655604