Get some local artisans to create a leather suit sized for Garfield? There’s no way Aslan is going to do that, as it would expose his secret shame to ridicule.
He’s freakin Jesus lion. They speak a word of it to anyone and they’re kitty chow. I mean that could be a great side plot to go along with the smut if you think about it. Aslan’s deep love for Garfield mixed with the shame of it, his efforts to keep everything out of the public eye. It could work.
Especially since the Narnia series is explicitly set in a multiverse. Narnia is a separate universe than the universe the Pevensies inhabit. And Aslan has no trouble crossing over for a bit to help out Eustace and Scrub near the end of the Lady and the Green Kirtle.
Get those green and yellow rings to Garfield, and get him into Narnia before it dies. Or, since worlds apparently merge in the afterlife, have the Garfield that died in that one Halloween strip show up in Aslan’s Real Country.