The only fanfic of them I know is "A Tryst at Midnight" on fimfiction(warning:nsfw!)
Maybe there's more but I just don't know
Bat ponies appeared in S02E04 and offical comic #09 as Luna's guards.
1. Thanks, time to go look it up so I can see it for once (still have yet to see half the episodes).
2. I just realized there is a small blush on Midnight Blossoms muzzle! xD