Try a machine shop supply house. You're looking for
"end mills".

Laguna tools also carries long, "reverse direction"
mortising bits.for the horizontal mortising unit
they sell. Their Robland X31 combinnation machine
needed them becuase the mortising chuch is on the
end of the jointer/planer cutter head. Robland
subsequently put a reverse switch on the jointer/
planer/mortiser head and took care of that quirk.

charlie b