I tried the entire process again just to make sure I'm not crazy, and unfortunately still getting the same 3 tk2d related errors 🙁 For due diligence I'll post them again:
Assets\Spine\Runtime\spine-unity\Asset Types\SkeletonDataAsset.cs(46,10): error CS0246: The type or namespace name 'tk2dSpriteCollectionData' could not be found (are you missing a using directive or an assembly reference?)
Assets\Spine\Runtime\spine-unity\Modules\TK2D\SpriteCollectionAttachmentLoader.cs(47,44): error CS0246: The type or namespace name 'tk2dSpriteCollectionData' could not be found (are you missing a using directive or an assembly reference?)
Assets\Spine\Runtime\spine-unity\Modules\TK2D\SpriteCollectionAttachmentLoader.cs(39,11): error CS0246: The type or namespace name 'tk2dSpriteCollectionData' could not be found (are you missing a using directive or an assembly reference?)
Still using the latest runtime package here Spine Unity Download (3_7-2019-02-15).
Help would be super duper great! Our animator can no longer use 3.6 apparently (he says it's forcing him to update to 3.7), but on my end I can't upgrade due to these errors, so our animation pipeline is at a bit of a standstill. Thanks!