You won't find a big pack capable of hauling the weight you're talking about that is lightweight. Just physically not possible to get a stout-enough frame, beefier padding, more robust construction needed in a pack twice the size of most UL packs. That said, for the kind of volume and weight you're talking about carrying, the weight of the pack becomes relatively inconsequential (horrors!).
A month's worth of food will end up weighing at least 40 pounds, plus a standard UL base of 15 pounds, plus packraft and accessories... I'm guessing you'll have a minimum of 70 pounds at the start.
Current production models would include the Osprey Argon 110, Arc'Teryx Bora 95, Gregory Whitney 95 or Denali Pro 105. Several mentions of Dana Design: the packs were awesome, but haven't been made for about a decade. As was also mentioned, the guy who made Dana packs now runs Mystery Ranch, and they make some huge, burly, Dana Design-influenced packs. MR has a fair bit of military contracting, so you know they'll take the load. No dealers for MR, though... have to deal direct.
Edit: Whaddya know... a fellow BPL'er kindly pointed out this website:
I called MR a year or two ago to establish a dealership, but they informed me they were switching over to purely direct sales. I guess a few of their original dealers are still floating around?