Anyone can put together a pretty lightweight kit at REI but of course the needed bits are lurking in the shadows amongst the mountains of pedestrian stuff. I take it from a glass-half-full point of view that it's there at all, all backed by their customer service policies.
They have all the clothing. They have light packs, shelters, bags, pads, stoves, pots, pans, stuff sacks, lighting, water treatment and storage, and other sundries. Few of these are bleeding edge lightweight but it would be easy to put together a nice lightweight kit from scratch in an hour on the Web site. If you live in the "right" market some of the items are even available in the store.
For the final jump to SUL you'd need to go to DIY or cottage gear makers for several key pieces, and that why we're here :-)