I picked up a Raptor 20 ga and a Vortex Crossfire Red Dot, which mounts on a Weaver or Pic rail, but I cannot find anything about where to cross reference an orderable rail that will mount on the receiver (that is already tapped)
Let me know if you've already added a mod to yours.
My Viper G2 Turkey came with a picatinny rail in the box. You can call them and ask if your Raptor was supposed to come with a picatinny rail. They have parts available and will sell you one if that model doesn't include the rail. Their number is 816-421-1400.
William at sumtoy can hook you up