Hi eliza_beth,
My husband used to work for that ShopRite on the IOM, and although they have the same name, they aren't related to the US company. The owner has some connections in the US, and used to fly over and bring stuff back with him. (But he's Manx all the way.) I don't know if he still does that, but you will probably find more American products than you will in Tesco.
How is life treating you on the island?
Take care.
Ellen