In the third season of Naruto Shippuden, Sora used Nine Tails chakra mode up to 4 tails, so why didn't Tobi capture him like he did with Kinkaku and Ginkaku?
Like Noted in the comments, Sora was a Filler only character. He does not exist in the manga at all, which the anime is based off of. His entire arc was just added in to lengthen the anime, buy time for the manga to progress, and make money. The Gold and Silver Brothers are in the manga as written by Kishimoto, and were the only source of 9 tails chakra Tobi ever got his hands on, which he
did use to create an incomplete 10 tails.
The Wiki Notes Sora's appearances are in the anime only, and lacks any time in the manga, supporting this.