MK 18/M4/M16/AR15

Links for the hardware

Germany: 

gearbox: V2 Gearbox M4 M16 QRS-System Delta Armory (softairstore.de)

hop up: CNC Hop-Up Kammer / Unit für M4 Series Type B (softairstore.de)

barrel: 6.01 AEG Barrel 310mm - Action Army (softairstore.de)

mag:  Delta-Mag M4 Midcap in Black (120 BBs) - Delta Armory | 43234202 (softairstore.de)

motor: G&G Ifrit 25K Motor - Long Type orange (25000rpm) | G-10-113 (softairstore.de)

battery: LiPo 11.1V 900mAh 15C Stock Tube Type - Mini Tamiya - Strike Systems (softairstore.de)

charger: B3 20W Lipo Battery Balance Charger / Ladegerät - Imax (softairstore.de)

silicon grease: ProTech Duo Pack Silicone Grease + PTFE Grease 2x 3,5g (softairstore.de)

silicon oil: ProTech Airsoft Silicon Öl / Silikon Spray 100ml | 43233055 (softairstore.de)

bucking: Super Macaron Hop Up Rubber 70° for AEG - Maple Leaf | 43218117 (softairstore.de)

tensioner: Maple Leaf Omega AEG Hop Nub Tensioner Solid Edition (softairstore.de)

USA/Canada: 

gearbox (just get a v2 gearbox, you can find many here): AEG Internal Parts, Gearbox, Version 2 Gearboxes - Evike.com Airsoft Superstore

hop up: EMG x Retro Arms CNC Machined Aluminum Rotary Hop-Up Unit for M4/M16 Series Airsoft AEGs (Color: Blue), Accessories & Parts, AEG Internal Parts, Hop-Up, M4 / M16 Series Hop-Up - Evike.com Airsoft Superstore

barrel: 

mag (just normal m4 mag): Krytac 150rd M4 Mid-Cap Magazine (Quantity: Black), Accessories & Parts, Airsoft Gun Magazines, Electric Gun Magazines, Shop By Gun Model, M4 / M16 Magazines - Evike.com Airsoft Superstore

motor: Matrix "Reloaded" High Performance Airsoft AEG Motor (Model: Long Type / Balanced Torque-Speed), Accessories & Parts, AEG Internal Parts, Motor, AEG Motors - Evike.com Airsoft Superstore

battery: Matrix High Performance 7.4V Stick Type Airsoft LiPo Battery (Model: 1000mAh / 20C / Small Tamiya & Long Wire), Accessories & Parts, Batteries, LiPoly / Lithium Cell Batteries, 7.4V Lithium Polymer Batteries - Evike.com Airsoft Superstore

silicon grease: Evike.com Silicone Grease for Airsoft AEG & GBB Pistols & Rifles (Model: Silicone), Accessories & Parts, Lube / Oil / Grease / Glue

silicon oil: EMG Made in USA 3oz General Use Silicone Oil Spray, Accessories & Parts, Lube / Oil / Grease / Glue - Evike.com Airsoft Superstore

bucking: 4UAD SmartAirsoft 4UANTUM Friction Pro High-Performance Bucking for Airsoft AEGs, Accessories & Parts, Hop-Up Buckings - Evike.com Airsoft Superstore

tensioner: RA-Tech Maple Leaf Precision Hopup Spacer / Tensioner for AEG Hop-up Units, Accessories & Parts, Hop-Up Buckings - Evike.com Airsoft Superstore