We do not have a dedicated Swift runtime that works on top of the standard iOS UI API, e.g. CoreGraphics etc. We do however have integration with cocos2d-x and cocos2d-objc. These are game engines maintained by 3rd parties with which Spine integrates. It should be possible to integrate both of these in a standard Swift app for iOS. However, we aren't experts on that topic, so you are likely to find more information on the respective websites and forums of those two engines.
https://www.cocos.com/en/products#Cocos2d-x