Heres a list of some of my favorite Nanofate doujins, given that Nanofate is at least 50% of the reason I got so into Nanoha:
All of MekiMeki Oukoku’s work is amazing, but particularly stand-out are the stories with Vivio as well. The way they mix MekiMeki’s ordinary focus on Nanofate’s flirting with Vivio being clearly tired of it is hilarious and also cute, especially since Vivio’s no better when Einhart shows up.
Nanashiki’s work is all fantastic, and they’re one of the few people still consistetnly making Nanofate doujins. I particularly reccomend their ‘You Are Like the Sun’ duology or the seasonal ‘Day’ works as a starting place.
Koguro is the other artist still regularly making Nanofate books, alongside some FuuRin stuff now. I adore their Owari Hajimeta Sekai no Hate ni book, which does a great job at portraying Nanofate’s relationship during the period where Nanoha was injured.
I like Furafura’s Recollections a lot, to the point that I scanlated it myself. The translation job is at middling as you’d expect from someone of my caliber, but I do encourage reading it if you’re interested at all.
Nagomi Kissa’s stories are funny, though they’re also quite sexual so bear that in mind.
Astllatte*Sorato’s art is odd but their stories manage to really capture the emotional core of Nanofate.
Tokoharu, Tama II, and Sagamani are also artists worth looking at. This is particularly true for Sagamani’s SANTA SANGRE, which is another approach to the period where Nanoha was injured.