Rectangular shaped hydration bladders : camping

Hey everyone,

Im looking for a hydration bladder that has a more 3D rectangular profile
like the sea to summit water cells. I find the standard flat hydration
bladders just turn into a cylinder when filled which makes packing
difficult. Alternatively I have found an adapter for the sea to summit
water cell that turns it into a hydration bladder as shown in the
picture ( but I am unable to find anywhere to purchase it so if anyone could help with that that would be great. Thanks!

r/camping - Rectangular shaped hydration bladders