I have compiled a list of sources for the elements that are available to the amateur chemist. Magnesium will be discussed here.
Magnesium is a light, relatively strong alkali metal. It is highly reactive but protected by an oxide layer. It finds much use in high-performance alloys that need to be light but strong. It is also used in pyrotechnics. Magnesium compounds are used as antacids, bath salts, and refractories.
In element form: Magnesium fire starters contain magnesium. Magnesium ribbon is easily obtained as well. Fresh water boat anodes are made of magnesium. Laptop frames, some car frames, and expensive pencil sharpeners are made of magnesium alloy.
In compound form: Epsom salts are made of magnesium sulfate. Milk of magnesia is made of magnesium hydroxide. Magnesium carbonate is used to make better grip when rock climbing.
Here is my sample of magnesium, a fire starter.