To find upgraded high-mounted stop lamps, follow these steps:

1. Check with Toyota Dealerships: Contact your local Toyota dealership to inquire about any official upgraded or aftermarket high-mounted stop lamp options available for the Land Cruiser 300.
2. Online Retailers: Many online retailers and automotive accessory websites offer a variety of high-mounted stop lamps designed to fit different vehicle models. You can search for options and read reviews to determine which one suits your needs.
3. Aftermarket Manufacturers: Some companies specialize in manufacturing aftermarket automotive lighting products. Brands like Philips, Hella, or Osram often provide a range of high-mounted stop lamp options.
4. Local Automotive Accessory Shops: Visit local automotive accessory shops in your area, as they may carry a selection of high-mounted stop lamps or be able to order them for you.

When selecting an upgraded high-mounted stop lamp for your Toyota Land Cruiser 300, consider factors such as compatibility, the type of lighting (e.g., LED or traditional bulb), and the design that fits your preferences.

Make sure that the high-mounted stop lamp complies with safety and regulatory standards in your region. Installation should be done by a professional or someone experienced in automotive electrical work to ensure proper functioning and safety.

Please note that product availability and specifications may have changed since my last update in January 2022. Therefore, I recommend checking with the latest sources, including Toyota dealerships and online retailers, for the most up-to-date information on upgraded high-mounted stop lamps for the Toyota Land Cruiser 300.