Try posting in the 100 section. There are lots of people with them sitting around their garages you could likely have for the price of shipping. That's how I got mine. The mods will get pissed about non-tech post and send you to the 100-series wasteland that is the Parts Classifieds, but phrase the title such as "Need OEM 100 series springs for Sequoia lift - will it work?" to keep it tech. And the springs must be similar dimensions T/B as people run 863/865/866's on 100 seriers rears. I'm using 80-series spacers in the rear.
btw, what year Sequoia are you lifting, and what are you doing for the front. I'm slowly in the market for another car, and have been considering another 100 series or a Sequoia. Are you just using Tundra front-end parts?