Muhammad Ali and Larry Holmes Sonny Liston and George Foreman Lennox Lewis and Mike Tyson Floyd Mayweather and Pernell Whitaker Anthony Joshua and Wladimir Klitschko (seems all top heavyweights sparred him) Try and keep it elite of elite. Not interested in Zab Judah sparring Joshua Clottey for example.
Paquaio and Porter Haye and Wilder Jacobs and Derevyanchenko Golovkin and Canelo Froch spared Groves, Degale, Eubank Jnr at different points of their careers, Groves also spared with Kessler in prep for Kessler second fight with Groves. Tyson and Holyfield Bradley and Crawford
Probably doesn't live up to your criteria of elite but i'm gonna post it anyway since i was there to witness it and it was fun to watch: Kessler sparring Groves, Skoglund and Nathan Cleverly before Froch 2. I heard Kessler sparred Skoglund again before his intended comeback and gave him such a whooping that he went straight home to Sweden haha. Skoglund then went on to give Callum Smith a close fight. Anyway it was fun to watch. Mikkel is a GREAT humble and fun guy, the others semmed cool as well.
You are as good as your sparrings/teammates. You cant basically be a top fighter if you dont spar top fighters. Maybe there are some fighters who could, but 100% sure that not many. Pro fighters need to stick this on their heads. And if they need to move and go living to another country/city to get better sparrings/teammates, they must do it if they want to be great. Sparring nobodies and training with nobodies all you will achieve is to be a nobody. Sad, but true.