after many years of wandering the abyss and conversing with oriental merchants in their dialect of english, I have found only one option for using YPbPr with a 3.5" screen: the MST703 LCD driver ic supports YCbCr and YPbPr according to this datasheet. It also appears to have automatic video...
So there's this little 5 inch screen you can find on ebay by a company named "Eyoyo". This screen accepts 480p/480i/240p component in natively, which is dope. (No interlaced VGA tho, sadface) I put one in my AtarWii Liinx and it's so good! It has a few quirks to it that can make it hard to work...