Mostly money... Flexible Specialties are pay only right now.
I'm assuming you've figured that part out, and gotten a Precision Arrows Flexible Specialty, then gotten it to level 20.
Now you need another one, or two or three (11.1% chance at $100 US per chance), and will need to "Disassemble" it/them to get the pieces required to take it to the next level.
Mostly money... Flexible Specialties are pay only right now.
I'm assuming you've figured that part out, and gotten a Precision Arrows Flexible Specialty, then gotten it to level 20.
Now you need another one, or two or three (11.1% chance at $100 US per chance), and will need to "Disassemble" it/them to get the pieces required to take it to the next level.