It may not be realistic to buy semi-finished products of McDonald's and KFC online, because the recipes and proprietary ingredients of restaurants are usually confidential and will not be sold to third parties. If you want to cook fast food like McDonald's and KFC at home, you can try the following methods:

1. Search and collect related recipes: You can find many recipes similar to fast food restaurants online. You can search for recipes like "home version of McDonald's hamburger" or "homemade KFC fried chicken".

2. Buy the corresponding ingredients: Some fast food products need special condiments or tools to make them taste similar. You can buy the required ingredients and condiments through online shopping platforms such as Taobao or offline supermarkets.

3. Learn the production process through video: Some chefs will publish tutorials on online video platforms such as blogs or YouTube, and introduce the production methods of various fast foods in detail in the video.

Please note that fast food may have a negative impact on your health, whether you cook it yourself or buy it in a restaurant. It is suggested to eat in moderation and enjoy delicious food under the premise of controlling diet. In addition, if you are new to cooking, please pay attention to food safety and hygiene to avoid food poisoning or other adverse effects.