FIX or REPLACE WHAT'S BROKE:
Periodically test your components, with a suitable meter or other instrument, to see if they're in good condition, and functioning properly. It's common (especially with old kits like this) for an experimenter to have blown a component or two (or more) without realizing it. And sometimes there's one that's defective from the start.
Just keep in mind that most components have a certain amount of "slop" in them:
Their component's official or marked ratings may be very precise,
but the component, itself, will probably only be approximately that value.
The range of acceptable or intentional variation of a component, or a circuit, is called its tolerance. Many resistors, for instance, have a "tolerance" of plus-or-minus (+/-) 20%. (A resistor marked as "100 ohms" may actually be anywhere in the range between 80 and 120 ohms.)
REPLACEMENT PARTS are available (usually cheaply) from:
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LOCAL STORES: Electonics hobby or pro shops, like some Radio Shack stores (yes, a few still exist), and some industrial-supply distributors. Ask a local electronics technician, ham radio operator, electrician or appliance repairman where to go.
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ONLINE retailers and distributors (industrial pros turn to Mouser Electronics, DigiKey, Grainger Supply, and others).
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BASICS -- Wire, switches, bulbs and other such basics -- can be found in hardware and auto-supply stores (and the staff can be helpful in finding the items), and sometimes in such departments at department stores. And these devices can be great basic experimenting tools to add to your kit.
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RECYCLE: Some parts can be "cannibalized" from junk equipment, or from cheap, new stuff. I've scavanged low-power rechargeable batteries -- and solar panels, and LEDs -- from cheap two-dollar yard lights sold at the local dollar store. Just be sure to test these scavanged parts, before using them, to ensure they'll work as you hope. Don't replace faulty parts with more faulty parts.