I have seen designs of electron sources that use a heated filament to create a cloud of electrons then apply a voltage across them to accelerate them for whatever purpose. Could you replace the filament with a needle spraying the electrons?
When you say "spraying," what do you mean? You could use an electron source of any shape you'd like -- needle, filament, whatever -- once you collimate and accelerate the beam, it no longer matters what the original shape of the source was.
The reason why a filament is used is just because it's easy to heat one up by passing current through it. It'd be harder to design a way to heat up a needle.