I asked around at two auto parts stores and nobody heard of one. I heard about it on here, but haven't found any. This OEM branded grease gun I bought has a 4 jaw coupler on it and you could put it on the zerk fitting, but you needed to grab it with a pair of pliers and hope you didn't break off the zerk fitting in the process. I just went to oreilys and got a different brand and this one has 3 jaws and it still a little hard to remove, but usually comes off okay if you move it back and forth and rotate at the same time. I've never had this problem before honestly, but then again this is the only grease gun with a flexible hose, so maybe that's why. The other ones I can just grab the entire grease gun and pull it off..
I didn't find the right solution from the Internet.