Did you ask them anyway? Doesn't hurt to ask if you haven't.
They're closely controlling the supply of the replacement headsculpts by making people jump through hoops and pay their own shipping to send the head in for the exchange. They want to prevent people from selling just the sculpts by themselves.
I don't think you'll find it being sold much on its own. That would leave them a figure without a head.
Someone posted a link earlier in the thread that this store* is selling the figure with the new head. If it really bothers you and Sideshow can't help you, you may have to just buy the figure with the replacement sculpt from there or another store that's done the exchange and sell the one you have.
https://popcollectibles.store/produ...dgame-ironman-mark-85-with-updated-headsculpt
*I have zero experience with this store so I don't know how they are.