So I did my own research about Flying devil fruits, and YES! it looks like there are more than 5 "real" flying devil fruits.
Zoan
- Tori tori no mi, Model: Falcon - Pell
- Tori tori no mi, Model: Phoenix - Marco
- Tori tori no mi, Model: Eagle - Buzz (One Piece 3D: Straw Hat Chase)
- Tori tori no mi, Model: Nue - Toratsugu (One Piece 20th x Kyoto)
- Mushi mushi no mi, Model: Kabutomushi - Kabu
- Mushi mushi no mi, Model: Suzumebachi - Bian
- Ryu ryu no mi, Model: Pteranodon - King
Paramecia
- Fuwa fuwa no mi - Shiki (One Piece Film: Strong World)
Logia
- Gasu gasu no mi - Caesar Clown
- Moku moku no mi - Smoker
Unknown devil fruit but can be flight-capable
- Dragon fruit - Kaido
- Crow fruit - Karusu
Flying devil fruits because of "Creativity" of user + Surroundings
These are fruits that can be flight-capable with some creativity of the user on using his devil fruit abilities and his surroundings
- Ito ito no mi - Doflamingo
By attaching string to the clouds
- Zushi zushi no mi - Issho (aka Fujitora)
By lifting the boulder while he is on top of it
Flying devil fruits because of "Creativity" of the user alone
I separated these fruits because I think there are debatable if real flying devil fruits or not. Listed here utilizes only their creativity in using their devil fruits abilities and not depending on their surroundings. What I mean here is that if you eat these fruits you will not immediately able to fly unlike the "real" ones, you need to think outside the box in order to fly. A great example of this is Gomu gomu no mi - Luffy.
- Guru guru no mi - Buffalo
Spins his hair like a propeller
- Buki buki no mi - Baby 5
Transform to a missile
- Buku buku no mi - Charlotte Mont-d'Or
Able to make books fly and use it as a foothold
- Gomu gomu no mi - Monkey D. Luffy
Using his gear fourth
Pell: You're lucky to see this. Only five flying devil fruits are known to exist
Maybe when Pell said this he is only referring to the Tori Tori no mi? After all, we already saw 5 kinds of this fruit, but the other one looks like not able to fly, the Tori tori no mi, Model: Albatros whose current user is Morgans. If this is true then maybe we can see another variant of this fruit that can fly in the future.
If not, then maybe the 5 known flying devil fruits are from the big shots like Marco, Kaido and others since these guys are famous in the world of one piece.
If that is still not the case, then maybe at the time that Pell said that then there are only 5 flying devil fruits listed in the "book of devil fruits" since we know that this book doesn't contain all the devil fruits as we saw in the Enies Lobby Arc when Kaku and Kalifa eat their "unknown" devil fruit at that time
Sources:
One Piece Wikia
Youtube Video about flying devil fruits