Not according to this link here
. Besides, Sai are not knives... They are originally tines for farming forks/pitch forks. In fact, all of the Okinawan Style Karate weapons in Kobudo/Kobujutsu originated from the use of farm tools. The Nunchaku are originally rice flails. The Kama are farming sickels. The Bo could have been any type of utilitarian dowel or rod used for carrying food or hanging clothes. This was done because the regular peasantry (not part of the Samurai or military class) was not allowed the use or possession of Swords.
True, Ninjutsu does incorporate weapons training (which may include use of the Sai). However, I think it would be easier to find a Karate Dojo that is reputable that includes Kobudo or Kobujutsu training. Like I said, not all of them include training in the weapon arts.