Side mounted sword.
The item id for Bayonet in unturned is 1438. You can use this ID with the commands below to spawn the item, give it to a player or buy it on a modded economy server.
Size_X: 3
Size_Y: 1
Size_Z: 0.25
Blueprints: 2
Blueprint_0_Type: Tool
Blueprint_0_Supplies: 1
Blueprint_0_Supply_0_ID: 1438
Blueprint_0_Outputs: 1
Blueprint_0_Output_0_ID: 67
Blueprint_0_Output_0_Amount: 2
Blueprint_0_Build: 27
Blueprint_1_Type: Tool
Blueprint_1_Supplies: 1
Blueprint_1_Supply_0_ID: 68
Blueprint_1_Supply_0_Amount: 4
Blueprint_1_Tool: 1439
Blueprint_1_Level: 2
Blueprint_1_Skill: Craft
Blueprint_1_Build: 27