Fallout – Does the built-in radio at Castle work as a recruitment beacon

No, the game only checks if there is a beacon in a settlement.

Only happiness increases the chance.

Build bars ( lvl 3 restaurant) to get +40 happiness.

No new settlers will come if you have five settlers that are not assigned to anything.

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