I suggest increasing the drop rate of the visage items while on a slayer task. The current is essentially 1/10k across the board with the exception of black dragons in the wildy dungeon, kbd and vorkath, and rune dragons at 1/8k adamant at 1/9k. So I'd suggest the following ( all of my below proposed rates are while ON A SLAYER TASK) this effect currently only applies to revenants and the wilderness weapons. So in my opinion a reasonable change would be as follows.
Draconic Visage
Rune dragons - 1/3000
Adamant dragons - 1/3500
Mithril dragons - 1/3500
Steel dragons - 1/4000
Iron dragons - 1/5000
Brutal Black Dragons - 1/3000
Black dragons - 1/4000
Brutal red dragons - 1/3500
Brutal blue dragons - 1/5000
King Black Dragon - 1/2500
Vorkath - 1/2500
Wyvern Visage
Ancient Wyverns - 1/2500
Spitting, Taloned, Long-Tail - 1/5000
Skeletal Wyvern - 1/4000
As suggested below and previously mentioned as a possibility I've moved Skeletal Wyverns to the Wyvern Visage section.
Skeletal Visage
Vorkath 1/2500