There are quite a few excellent manufacturers, so I'll go through my preferred list.
Sensei Phil Worbington manufactures each pair of sai to custom fit the user. When you're ready to order, he'll ask you to measure various parts of your hands and forearms. He really knows his stuff, being an expert in the martial arts, as well as a long time machinist.
Welcome to Worbingtonsteele professional hand crafted martial arts weapons
I have two pair of sai made by him, and they've both served me exceptionally well. The balance point is well-centered, being a little bit tip side (I refer to the center of the sai as the area where the handle, guard, and shaft intersect) which is what allows you to get a good flipping motion.
Since each pair is custom made to order, I don't think he keeps any in stock.
Kensho International:
Sai Kensho International
There are a bit less expensive, and aren't custom-made for each user, but they are of very high quality, and nicely balanced. The balance point is closer to the "center" that I described above. Some people prefer it at this "center," others prefer them slightly tip-heavy.
They should have them in stock and ready to ship.
Agena Energy Sai:
Energy Sai of Agena
(warning... the color scheme for that site is terrible)
The most expensive of the bunch. These seem to be a bit more tip-heavy than the Worbington sai.
They do offer some things that the others don't, though, such as a metal thread handle wrap instead of cotton threads used by the others. Again, some people like them, some don't.
Shureido:
Shureido USA - Sai
These will probably be the least expensive of the bunch. Not custom-made, but still of high quality, and excellent balance. I would take a bit of time to speak with the lady who answers the phone there, though. Very nice person, and also quite knowledgeable.
