part config file:

"Item Shortname": "door.double.hinged.metal",
"Skin Id": 2097638599

[Item Skin Setter] Config parsing errors:

- Skin with ID "2097638599" does not exist.

https://steamcommunity.com/sharedfiles/filedetails/?id=2097638599&searchtext=double+door+metal

as you can see in the link the skin id is right there clear as day and matches what i got

Correct, at the moment these are not supported yet, it's on my to-do list.

Where does it currently get the ids from?

The engine itself, you can look at the source on Github if you want.
https://github.com/thibmo/ItemSkinSetter/blob/main/ItemSkinSetter.cs#L128

Workshop skins can now be used in v1.1.4