In my expanded circle of local gaming acquaintances, most niche rpgs are for most practical purposes "nonexistent". It's only the few really hardcore rpg gamers, which are even aware of anything beyond D&D.
For example, many of the casual gamers in my local gaming circles don't even know what Pathfinder is.
I have to admit I haven't played a lot of niche RPGs lately. However, I have a circle of acquaintances with whom I know I could get enough for at least a one-off of most RPGs, niche or not.
However, I have had a strong gaming store in my area since '81. It has always encouraged gaming on site (either in the store, or in the attached game club) throughout it's history. It also was started by a circle of friends. It also is lucky enough to be in a college town (Newark, DE).
In my experience (direct and from visiting other stores while traveling), that is the perfect storm of having a vibrant gaming community.
1) A hobby gaming store - It keeps RPGs available and handy. It also is a business with an interested in #2 below.
2) On site gaming - Important for creating a community of gamers that interact. With community interaction and a place to play, you can experiment with a lot of RPGs to see what you like without having to buy them all initially.
3) A college town - College students are the ones who have the necessary time and interest in doing something like gaming. There is also a steady evolution of the gaming groups as some graduate and move away and others come into town and join the community (of course, many graduate and stay around at some level). Most of the very successful gaming stores I have seen over time have been in college towns.
I admit, a strong gaming club without a retail store can be a lesser substitute for 1 & 2 above. However, a lot of these tend to be somewhat limited (for example, college clubs usually require members to be students). Also, you can't underestimate the ability to play in a spot where you can buy supplies on the spot (I know many dice sales have happened because someone forgot their dice), or decided to buy and try a new game from wandering the store and discussing something on the shelf before or after a game.