Compression fittings are in the plumbing section of your local hardware store. Go to any Ace Hardware, Home Depot, Lowes, etc... and ask for them. In the states, you will have to use 3/8 fittings. Like Tinybaum said, just sand the inside out until it will slip onto the diff cup. Then super glue them into place. I think the linky above has all the details.