Yeah - after an extensive search I've not been able to find a retailer that still has the double wall version.
Please note, the lids are glass filled nylon... a plastic that 1) has yet to have any scare about leaching 2) isn't in contact with the liquid for an appreciable amount of time anyway. So, please, dispense with the knee-jerk 'plastic is bad' attitude if you haven't though it through completely.
Also, please do not state materially incorrect facts... Kleankanteens come, by default, with PP caps. SS Caps are an optional extra purchase.