What a shame. I know the customer is always right, but that engraver who chopped the trigger guard should be slapped upside the head!
I'd buy it if it was it cheap enough. The current stocks do look like they might be ivory and would bring big money here in the USA. I have no idea what sort of demand there is in Australia and they can't be imported here. Welding in a piece is probably the best option, but the gun would have to be reblued again. that work won't be cheap.
A custom set of target grips fashioned like the ones below are another option. You'd still know what's under there, but at least it won't look like a hack<saw> job.