Where can you buy an Aloe Vera plant?
Aloe Vera plants are available from most garden stores world-wide. However be absolutely sure you purchase the Aloe Barbadensis Miller variety if you want a plant where you can use the gel.
Note that outside of Mexico, the Southern states of the USA, Africa and Australia most plants are small and only really suitable for cuts and burns.
If you want a plant where you can take the gel out of the leaves for consumption you will need one about one to one and a half meters high with leaves of about 10cm width at the base.
Typically these will be 3-5 years old and you should always harvest the outer leaves first.