I believe Haro started to use 14mm axles stock on front and rear in 1996, after that it became the standard. On most flatland frames 14mm never really made it because the only real freecoaster available was Nankai 10mm...
Nowadays its hard to find 14mm flatland frames and forks but some companies are sticking with 14mm: Quamen, Hoffman Strowler, Magicfruits Exploit, Ares, Felt Dreamcatcher, Fly Tierra, Macneil Collier, S&M LAF, Dragonfly ... and more I can't remember.