They are plentiful in the Villa. They are carried by ghost harvesters who use them as their main weapon. Each ghost harvester yields 5 of them upon death.
Throwing knife spears can be used to repair both knife spears and knife spears clean. Owing to the thrown weapon's high health, as well as normally being found in perfect condition, this will repair either of the melee weapons to perfect condition.
They are limited once you return to the mojave.
They can be succesfully coated in Cloud Kiss (or any other poison) to provide additional damage over time.
When thrown in a first person view outside the Sierra Madre, the spear will have a trail of the cloud. This is possibly because it is commonly used by the ghost people.
The throwing knife spear has very high item health relative to most other melee weapons, and as such would degrade very slowly, even though you can only attack once with it as it becomes unretrievable once thrown.
Even though it is classified as a "throwing spear," it cannot be used toward the GRA challenge "You Don't Belong In This World!"
pcxbox360 Throwing knife spear is marked as a "Player Only" weapon, meaning it cannot be given to companions for use.
pcxbox360 Throwing knife spears are not affected by the Loose Cannon trait.
pcps3 If you throw one on a bear trap while crouching, it will explode.