There is a Nunatak Half Bag in the Gear Swap. Nunatak could prolly overfill the bag. I would still be less expensive and take less time then a new bag.
I like the romantic idea of huddled on the face of Eiger in a parka and half bag, but for general use it would be hard for me to keep my hands in the bag or parka pockets. Though it seems you are sold on the ARC AT quilt.
Feathered Friends also has their Vireo bag, maybe worth a look.