what file specifically does the hud icon come from, in that case?

Yes, I don't mind as long as you apply the same conditions of the license provided within the beta tweaks mod for the content you borrowed. This basically boils down to giving credit, including the license file in your mod, and making a disclaimer that people cannot just grab this content from your mod without asking for permission first.

This is mainly done to prevent reposts of reposts without giving proper credit as I have not had the best of experiences when it comes to this. Besides that, you should be good to go.

Is there anyway I could get just the hud icon for one of my own mods?

I made it myself using the weapon worldmodel and real gun counterpart as reference. If you are having trouble getting it to work in game, you will need to install the Ultimate Tweaks for Beta Aesthetics mod in your custom folder, activate the sub-mod for the weapon that comes with the Ultimate Tweaks mod (by also copy pasting it into the custom folder), as well as subscribing and set this mod with higher priority in your workshop load order.

Wheres the weapon icon for this model from?