it took king 107 chapters since his introduction to pull out his sword you gotta be patient my boy
Mihawk's black blade was touched upon in the second chapter after his introduction.
Ryuma's black blade was touched upon very soon as well, even before Zoro actually fought him.
In both cases, Oda took the time & patience to explicitly underline that these blades are special.
Ryukogyu himself is forgettable as fuck, let alone his "black blade" which got next to no relevance/respect/hype at all.