Where to buy: Helium is generally bought by wedding companies or ordered directly from chemical plants; Hydrogen may have to be ordered at special chemical plants. Sometimes you buy too little and people don't buy it yet!
When I need hydrogen, I usually make it myself. The principle is simple. Every city has a chemical market. I went to the chemical market to buy a bottle of sodium hydroxide (500g), which is about 10 to 15 yuan, and then I made a solution. Then I put the aluminum sheet on the fire, cool it and put it directly into the solution, which will produce hydrogen. Because it is burnt, there will be no obvious phenomenon at first.