Where Percy got Scabbers

[nineve_laguna]

No: HPFGUIDX 83709

Does any one knows where Percy got Scabbers? If he was his pet before,
he must have got Scabbers somehow, didn't he know, the humungous 
bighead, that it was "a common garden mouse", or was he in allegiance
with the Dark Side all along, the traitorous wizard.
Pets don't just appear out of nowhere, except cats, that is. But 
there is a mouse in my bed, I just keep it there? I don't think so. 
So, how did Scabbers become a pet, from a filthy pest?
Nineve