Kalphite soldiers, Aberrant Spectres, Tormented Demons, and Corporeal Beast are probably the most reliable monsters for blues. This doesn't mean your getting 50-75 blues/hr at those monsters like waterfiend crimsons. They just drop blues a bit more often then the other charms, but overall are very slow charms. On top of that your stats aren't in the efficient levels which makes hunting blues an even worse training route. I'd suggest slaying for charms because majority of slayer monsters drop a decent amount of charms. Other monsters you can kill for crimsons at your levels are Dust Devils (will have to get slay up), and Black Demons. Rock Lobsters > Waterfiends > Black Demons >> Dust Devils