I've been looking into this, and I don't think it exists. I have an Anbernic RG 405m, and have been testing TimeSplitters on it. On easy mode it's kind of playable, but certainly not comfortable and accuracy is atrocious.

So now I'm looking through lists of handhelds, and from I can tell, it looks like there just is no such thing as a handheld that is both pocketable and reasonable to play dual analog games on.

The closest might be the Retroid Pocket Flip (can't say for sure cause I don't have one), but I do not consider that pocketable.