In fact, Anker is one of those companies putting out GaN chargers and they have recently announced the Anker Nano II. This is the company’s latest GaN chargers and they are said to be not only more efficient, but also more compact than the previous generation. They are sold in 30W, 45W, or 65W options.
The reason why GaN chargers are so small is because of the use of GaN as the semiconductor, which removes the need for other components that can contribute to the overall size of a charger. They are also said to be more efficient if that’s important to you and will produce less heat.
These are all USB-C chargers which means that you would need a cable with USB-C on one of its ends. To date, handset makers haven’t really introduced GaN chargers to their lineup so you will need to look for third-party solutions, like those by Anker, for all your GaN needs.