Answer:
If you need to get a UPC (Universal Product Code) now known as GS1 for the purpose of selling your items in a retail Establishment that demand it, then you will need to register with GS1 and get the bar codes from them.
Other bar codes are very simple to get. Lets assume you need to get a bar code for your product ID. Use any label design program (I recommend NiceLabel Evaluation Software), simply choose the TYPE of bar code you want and give it the information you want to convert to bar code, such as Product ID and the software will do the rest. It will automatically generate the correct format of the bar code you need.