Britax B Dual - Lower Car seat adapter bar

Hello, 

I have purchased a B Dual pushchair for my bump & my Daughter who will be 18 months when baby arrives. I would really like the lower car seat adapter bar so that I can attach a car seat on to the bottom of the pram, but being a discontinued model I can't seem to find one anywhere. 

I've contacted Britax with joy, looked on Ebay & Amazon and a few other suppliers.  Anyone here able to help any further please?

Many thanks in advance - from one semi stressed out Mum x x x