Many teachers go abroad during vacations these days, and they can collect materials in English-speaking countries. TV and radio are good sources. They provide a variety of materials. The information is current and the language is natural, but the content has to be chosen carefully. Newspapers, magazines, advertisements, and other types of printed material are very useful.
Teachers can take photos, make video tapes or record audio tapes.
If they make plans before they go overseas, they may be able to make good video or audio programs. Even in your home country, you can browse the world wide web and search for useful materials for classes. The market of language teaching materials are fairly large, and many companies are competing. They produce new materials and promote them with many advertisements and through their salespeople. You need to be careful about what they tell you.