Finding sparring as a heavyweight is obviously hard due to less big, talented men being around. I imagine most elite heavyweights have crossed paths at some point. Joshua for example has sparred Wlad, Fury, Dubois, Hrgovic, Yoka, Joyce, Chisora, Price, Wach, Jennings, Bakole, Okolie. He's fought amateur or pro against Ruiz, Whyte, Povetkin, Parker, Breazeale, Martin, Takam, Dychko, Majidov. Wilder has sparred the likes of Wlad, Miller, Gassiev, Haye, Junior Fa. I doubt you'd see this in any other division.
You`re not meant to spar hard against each other, it`s just practise, who gives a crap if some guy knocked you on your arse 10 years ago? All that matters is when you`re in peak shape and ready for a big fight after prep for weeks or months, this sparring nonesense has to stop, it`s odd.
People can sniff each other out when sparring, its more than practice, you can see the inevitable winner 9/10 in sparring even if its light !