M4 style fire selector blank/delete

[Schnitz]

Hi all 

 

Someone managed to shoot my fire selector blank (not the selector, the disk on the right side) into my arp9 ?. It's split in half and popped inside the body. I could glue it back together but I can't imagine it would be an expensive replacement. I can't for the life of me find this part, although knowing me I'm looking for the wrong thing. Does anyone know where I could buy one of these? 

 

Thank you