By the bumper insert do you mean these ones?
https://www.ebay.com.au/itm/23480122...3ABFBMjo-dkbJj
Theres a few of the side ones available at a quick glance, I'm sure the centre strip would be out there too with a bit more digging.
This could be an option, pricey but you may be able to re-coup a few buck selling the rest of the bumper locally. Although if you see the prices of the over riders alone its not actually that bad.
https://www.ebay.com.au/itm/27546306...Bk9SR_z1jNaxYw
With the over riders theres a couple of types to look out for, the Ghia style ones you're after are probably the easiest to find, they'll have the cut out for the bumper trim like this one.
These are the Rallye pack style without the cut out.
The other difference is the edges, on Ghia and Rallye pack they either have a scalloped edge like the first one or an angled edge like the second and varied between the two over the years.
I'd be trying Yesterford or any other small Ford specialists you can find locally and gumtree.
Classic Ford Forum would be worth a try too as with the UK sites like Turbosports and Oldskoolford.
Good luck with it, sounds like it'll be a nice car when you're done.