Stand Alone Super Tweeter for Revel F208?

Townshend Maximum Super Tweeter -around $1599 full retail (musicdirect.com).

Townshend is a good choice, as is the Enigmacoustics Sopranino

I do however have to note that a super tweeter should not add "sparkle" to your speaker. If you can hear the effect of a ST as sparkle you probably have the cross over set too low or the ST level set too high. The ST should be heard more as a tightening of transients and a greater appreciation for the space in the recording. You shouldn’t actually be hearing the ST (unless you are a dog or a teenager)

I feel like the Revels could use more air. Things like triangles, bells etc. are there but they aren't as sweet as the other speakers I mentioned.

Triangle would be one of the candidates, but other instruments have even more energy above 20KHz -- this is a very interesting article on the subject
https://www.cco.caltech.edu/~boyk/spectra/spectra.htm