Fallout – find the Vault-Tec lab coat

There are a few sites (like this one) that have lists of source materials for copper. I basically pick up everything I can and take it back to my workshop for scrapping. Most of the items that contain copper seem to be electrical items, like lamps/fuses, hot plates, etc. I keep an eye out for those items while I'm scavenging.

Regarding the "large quantities" part, I think that's the challenge. I've been roaming for quite a while, so I've picked up quite a few toasters and hot plates/etc, but they never have tons of copper. It's just a constant struggle to keep an eye out for it.

For reference, I'll repost them here.

Acid – Abraxo Cleaner; Anti Freeze Bottle; Suprathaw Antifreeze;

Adhesive – Duct Tape; Sealed Wonderglue; Vegetable Starch;

Aluminum – Coolant Cap; Distress Pulser;

Antiseptic – Abraxo Cleaner; Turpentine; Abraxo Cleaner;

Asbestos – Biometric Scanner; Coffee Pot; Extinguisher; Oven Mitt; Pack of Cigarettes; Teapot;

Bones – All Bones (ex: Tibia); Animal Parts and Corpses

Broken Light Bulb – Street Lamp;

Ceramics – Bathtub; Toilet; Ceramic Bowl; Coffee Cup; Sink; Teapot; White Plate;

Circuitry – Alarm Clock; Distress Pulser; Enchanted Targeting Card; Military-Grade Circuit Board; Telephone; Hot Plate;

Cloth – All Dresses, Suits and Outfits (ex: Laundered Green Dress); All Hood and Hats (ex: Hood with Straps); Box of San Francisco Sunlights; Cigar Box; Couch; Kitchen Chairs; Pre-War Money; Last Edition Newspaper; Pack of Cigarettes, Paintbrush; Rug; Trifold American Flag;

Cork – Antique Globe;

Copper – Fuse; Hot Plate; Light Bulb; Power Relay Coil; Telephone; Vacuum Tube;

Crystal – Camera; Microscope; ProSnap Camera;

Fiberglass – Abraxo Cleaner; Cigar Box; Jangles the Moon Monkey; Telephone;

Fiber Optics – Biometric Scanner; Microscope;

Fuse – Street Lamp;

Gears – Adjustable Wrench; Camera; Desk Fan; Gold Watch; Microscope; ProSnap Camera; Typewriter; Silver Pocket Watch;

Glass – Beer Bottle; Empty Milk Bottle; Fuse; Glass Pitcher; Lamp; Light Bulb; Nuka Cola Bottle; Shot Glass; Vacuum Tube;

Gold – Gold Items (ex: Gold Watch, Gold Lighter);

Leather – All Hides and Leathers (ex: Radstag Hide); Some Arm and Leg Pieces (ex: Leather Left Leg); Gas Masks; Harness

Nuclear Materials – Alarm Clock; Biometric Scanner; Distress Pulser; Nuclear Material;

Oil – Blue Paint; Flip Lighter; Gas Canister; Oil Can; Soap;

Plastic – Automatic Institute Pistol; Bread Box; Enchanted Targeting Card; Files; Plastic Spoon; Pack of Cigarettes; Shopping Basket; Scissors; Anti Freeze Bottle;

Rubber – Baby Bottle; Fridge; Street Lamp; Tire; Extinguisher;

Screw – Antique Globe; Desk Fan; Hot Plate; Typewriter; Toy Car; Toy Truck; Antique Globe;

Silver – Silver Items (ex: Silver Fork; Silver Locket; Silver Bowl); Enchanted Targeting Card;

Spring – Spring; Camera; Flip Lighter; Kitchen Scale; ProSnap Camera; Typewriter;

Steel – All Pistols and Rifles (ex: Pipe Auto Pistol); Ball-peen Hammer; All Melee Weapons (ex: Tire Iron); Some Armor Pieces (ex: Raider Left Arm); Blue Paint; Extinguisher; Flip Lighter; Gas Canister; Kitchen Scale; Mailbox; Oil Can; Radiator; Safe; Shopping Basket; Screwdriver; Scissors; Stove; Street Lamp; Toy Truck; Turpentine;

Wood – All Trees (ex: Maple Tree); Wooden Objects (ex: Table); Ball-peen Hammer; Box of San Francisco Sunlights; Cigar Box; Paintbrush; Picture Frame; Screwdriver; Trifold American Flag

Plasma weapons in Fallout 4 are relatively rare because of how powerful they are. You'll almost certainly not find one before level 20 and if you do you'll most likely be out of ammo for it with no way of getting more as the plasma cartridges are some of the most expensive ammunition in the game. Ultimately random drops are random and so you may find them anywhere, higher level enemies are far more likely to carry one than lower level enemies though.

You're far more likely to find a plasma pistol than any other form factor, but this can be upgraded into a rifle using the weapons bench as required, and to that end, there is normally a plasma pistol being stored inside the Mass Pike Tunnel West (near Diamond City), inside the room containing a steamer trunk with a Plasma Pistol inside.

The "best" plasma weapons in the game are the unique faction variants such as Experiment 18-A, which can be purchased from a synth vendor in the Institute, and the AX90 Fury or Sentinel's Plasmacaster, which can be purchased aboard the Prydwen.