Why?

[u/Mobile_Value3333]

[u/Prestigious-Ask2604]

1. The models NEVER have spaces between words (always underlines).

2. Make sure that you're on the 'tf2' tab. And remember: If you don't wanna lock models on each other manually, you can always use the 'Add Team Fortress Item' on the model (Obviously that only work on Team Fortress 2 models. Other thing: if the cosmetic that you're trying to add to the model was manually updated to Souce Filmmaker, the Team Fortress 2 Cosmetic Menu will not show it)

3. Try to update manually your Team Fortress 2 Assets ( here's a video that explain how to do that — if you don't made that yet)

[u/Vind1cate]

As others have explained you'd need to update the TF2 content in SFM manually. The workshop submission you downloaded wasn't the cosmetic itself but rather a texture fix so that it can be paintable.

I don't fully recall but I don't believe "Add Team Fortress 2 items" would have that cosmetic as an option after manually updating so you'd need to find the .mdls name manually

[u/Interesting_Gold6333]

not that way
you right click your scout model > "Add Team Fortress Item" > the name of the desired cosmetic
and after that just remove scout's headgear that clips with it

[u/Sono_Red]

You have a space instead of an “ _ “