Hmm, are you using C#? I could try looking around for an API. I've done some work with Unity in the past so I might be able to help in some capacity.
Assuming that's impossible, though, the problem I'm running into is that it's hard to find unique frequencies for each notes. Each frequency is often shared between some number of notes when I play them, so it's pretty tedious trial and error, made worse by how difficult it is to identify frequencies when it keeps flipping between the highest peak. What if, instead of displaying only the current highest peak, it displayed multiple (like the top 5)? That seems like it'd be pretty doable with what you've already got so far, and would make it a lot easier to identify the different frequencies in each note. If possible, it'd also be cool to order the frequencies by their frequency number, instead of by highest peak, so that they don't flip-flop whenever one peak gets slightly higher than the other, since it can be really hard to read on the current display when two frequencies are at similar peaks.