When I picked up my telescoping disc retriever a couple of months ago, it had a dual-fork and a rectangle attachment included. One of the reps at GGGT told me about the suction cup ball attachment, but they were out of stock at the time. Last time in they had them in two bolt sizes, 5mm and 6mm. I was able to look at the retriever I had previously purchased and the 5mm attachment worked for me. I have tested it on some dry disc and it works. Not sure if it will be much use in deep, dirty ponds that moron architects are putting onto disc golf courses today, but if you can see your disc, the suction cup retriever is going help a lot. Dirty deep holes will still need you to drag the bottom until you can feel your disc.
I am happy to have the new attachment in my bag :)