You arent the first to ask for this regarding vanilla weapons.

If you can bribe an animator to make you a full animation set, then it's a matter of your budget.

Though I will warn you that vanilla weapons which share the M4A1 hold animation (CAR4, AMCAR, AMR16, Eagle Heavy, AK Gen 21 Tactical, AK5) will be a headache. The thumb might float in the air above the gun, or be sticking through the top of the receiver/handguard, or you'll have to accept the animation won't fit perfectly for everything.

I ran into these issues a few times when trying to apply my URGI animations to an AR18 like the Spear LT.