Very good question Johnist ,I was thinking same thing I would not mine buying them from crowned shop ,I tired to go to where they are drop but there are so many players trying to win these pets I was not able to.
Not sure why they say crowns only, but they are dropped pets.
the ianthine spectre drops from gurtok demon in the plaza of conquest, ds, and the crabling is said to drop from crazed forest spirit in ms.
They say 'Crowns Only' because they are a special breed of pet that is intended to be bought with crowns or won as a drop. Almost every piece of gear that is 'Crowns Only' (This includes pets) is available as a Drop.
I knew where those were available as Drops. I was wondering where they would be available for purchase so that I would know how much crowns I would be saving myself by getting them as a drop.