I remember fueling up my Cessna 150 with red 80/87 octane. It’s no longer available.
Why?
Because the avgas market is so small. Splitting it into two even smaller pieces didn’t make financial sense.
With 80/87 (red) and 100LL (blue), an FBO has twice the number of pumps to buy and maintain. But one pump (blue) outsells the other by over 2-to-1. Now they have a pump (red) that costs just as much as the other, but sells less than half the volume. Which means the cost per gallon will go up a bit due to the lower volume. And you can’t sell more of it because the red only works in some planes, but the blue stuff works in everything.
It didn’t take long for the industry to settle on one pump selling 100LL.
Now, 91UL is a bit different, being essentially a by-product of mogas production so it’s already widely available. But as others have pointed out, it likely only makes sense for an FBO to put in a second pump for it if there’s a large population of low-compression singles based at their airport.
Why don’t you talk to your local FBO and ask them what they would do?