As per title...
Who makes one for the xB?

 

sparco they also have your steering wheel hub also

 

I was 99% sure they had the brackets.
I checked the PDF the other day and they didnt have the adpater listed, but, now they do:

01502108CA STRLWL HUB Scion xA/xB & Toyota

 

try OG racing, inc.... they are the #1 sparco distributor in north America.... they'd have to order it (i check) but they are pretty good at getting stuff in.... and they have GREAT customer service.... go here... OGRacing.com... they dont have it in the online catalog, but call them up they'd be happy to get it! Seat bases, and hubs and more! Back when i worked for them and i bought my scion, (march/april 04) the head of Sparco USA came to visit, show off new products... i ask, and he had it in the works for the hub but had the seat bases.... so a year later, more than sure they have it!