I can help you with information about Spine bone icons, but I'm not able to help with Stream Deck-specific icon resources, as that's not related to Spine.
Regarding Spine bone icons:
If you're looking for bone icons to use within Spine itself, you can select from the built-in bone icons in the editor. The most recent versions of Spine have even more bone icons available. However, currently you cannot upload your own custom bone icons - you can only choose from the pre-built icons that come with Spine.
If you'd like to see specific bone icons added to Spine, you can suggest them, though the team would need to manually add them to the editor.
If you need Spine branding images for other purposes, you can find official Spine logos and branding materials at:
https://esotericsoftware.com/branding
You're welcome to use these branding images as long as you follow the requirements listed on that page.
If you have questions about creating custom icons for Stream Deck or other third-party applications, I'd recommend checking the documentation for those specific tools.
