Hey brother, the only company I am familiar with that makes a bandolier/sling is BLACKHAWK! I am sure many other companies have made them.
I do not own one but have worn one loaded to bear with 00buck. It was not what I expected. It was heavy, uncomfortable and an all around inconvenience. Granted with tactical gear, such as a vest and/or a chest rig maybe it would have worked better? Not sure. I would recommend a regular sling your preference on Points. Look into other ways to carry shells, such as on the gun or in pouches attached via MOLLE to a vest perhaps? Thats my humble opinion.