Aside from more fighters moving down from Bantamweight, which has been of great help recently, the UFC must move more quickly in building the talent pool for the UFC Flyweight division.
Although the Heavyweight division is arguably as weak, there is enough volatility with the fight results to ensure that the competition remains relatively fresh. At Flyweight, with Demetrious Johnson being on such a quality run, the lack of depth is already apparent as his next opponent is sitting at #14 in the UFC Flyweight rankings.
The following fighters may be not-so-obvious options for additions to this division as they don’t have undefeated records and aren’t spending time in major or mid-major promotions, at least not in the states.
#15 – 
Yuki Motoya (24) [12-4-0]
I’ll be the first to admit, the ratings are possibly being a little too kind to Motoya. He’s got a unique combination of characteristics that always yield a friendly rating; he fights and wins often and he fights aging fighters who’ve recently dropped down in division, likely out of desperation.
However, he’s young and 9-1-0 in his last 10 (with the lone loss being a split decision that he since avenged). I think you have to give him at least a glance.
#18 – 
Czar Sklavos (32) [10-3-0]
I’m somewhat shocked that I hear nothing about Sklavos. He got a late start to the game, debuting and losing to TJ Dillashaw back in 2010. And although he’s recently lost two, one to #16 Sampo and the other to former top Flyweight Alexis Vila, he’s on quite a run. His next fight sees him once again travel across the Pacific to fight #28 Ogikubo. I wouldn’t be surprised if a win here yields a phone call from the UFC. At the very least, he’s racking up frequent flyer miles.
#27 – 
Giovanni da Silva Santos Jr (27) [15-1-0]
Having only lost his debut fight, “Soldado” is the top-rated Brazilian Flyweight that still remains undiscovered by a major promotion. His last win over former #2 Strawweight Gilberto Dias launched him up near the top-half of the first page of the Flyweight rankings. Due to a lack of data, there is a tendency to underrated these types of Brazilian fighters who never leave home. As a result, he might be one to watch.
Honorable Mentions: #32 – Nildo Nascimento, #43 – Yuya Shibata