Not sure what you are after but things like the katadyn Hiker filter come with a wide Nalgene adapter. See the picture here...
Is that the sort of thing? Not sure where you can get it as a part though. If you know someone with a 3D printer they can probably make you something...you want it in ABS not PLA.
Then there is this...
that claims to come with a Nalgene adapter. Bit pricey for just that bit though.
Thanks @OldGuyot. The "Source Outdoor SNEP Convertube Water Bottle Adapter Into A Hydration System Kit" has received a lot of critical reviews on Amazon.
I want to make a gravity water filter installation with the following scheme, from top to bottom:
1. Lightweight plastic (dirty) water bottle, with air-valve and extending hose-barb
2. Piece of food-grade silicone or PVC hose (1/4" inner diameter)
3. Grey Sawyer Inline Hydration Pack Adapter
4. Sawyer Squeeze Water Filter
5. Blue Sawyer Inline Hydration Pack Adapter
6. Piece of food-grade silicone or PVC hose (1/4" inner diameter)
7. Katadyn Active Carbon Bottle Adapter
8. Piece of food-grade silicone or PVC hose (1/4" inner diameter)
9. Lightweight plastic (clean) water bottle, with air-valve and extending hose-barb
Hmmm, sounds like a rather involved set-up. Have you considered a Katadyn Gravity BeFree Filter ( https://www.rei.com/product/139666/katadyn-gravity-befree-water-filtration-system-3-liters) or even taking a standard Camelback, cutting the drinking line in half, and inserting a Sawyer or Sawyer mini in between the two pieces of tubing? I have used both set-ups, the Katadyn and Sawyer insert. The Katadyn is great for both on the trail filtering and in camp gravity feed, and the Sawyer setup lets me drink right out of my Camelback while on the hoof.
Good luck and see you down the trail!