Mando Mercs Costume Club - Yes, modified Nerf Guns can be used as approvable costume accessories, but the key word is MODIFIED and non-functional. Note the amount of changes made to this
The Best NERF Guns to Modify | Blaster Piece
Nerf gun upgrades! Mod your nerf gun with a Raspberry Pi
Nerf Gun Mods - Instructables
SSWI Modded Nerf DoubleStrike SHREDDER Tactical Barrel – Double Strike Mods – So Sick With It