http://www.dodgeandburn.com/collections/shop/products/six-by-seven
I have got one and found that the textile quality is good and it looks cool. Below are two snapshots with my 645N SLR camera (taken with my *Pentax* K-5 + DA35):


Btw, the original Pentax 6x7, together with the original Pentax 645, are recognised as one of the milestone cameras of Pentax by AOHC whilst my 645N is recognised as a masterpiece. So, why not a 645 T-shirt also? Besides, I would want more colours of the T-shirt instead of only that light cyan colour for the background to "select" from, nonetheless.
Related:
True Fanboyism!
20 Millions of Pentax Cameras in 2013
The 645D Kit (Lens) Got Delivered to an End-User, Finally!