Hi,
You'll need to be very lucky, they've disappeared from the Tabbert T@B web-site - so I assume they've stopped manufacture - and in Holland (I work in Rotterdam) where you do see quite a few single axle T@B about - none of the dealers (or the Marktplaats "for sale" web-site) have an XL for sale.
And I know that people in the UK haven't bought as many T@B as my friends in Holland.
Good luck with your hunt. Robert