Sounds like a plan Michael.
Of course, you will now also need the underside crosses, but when (not 'if' ) Airfix send the decals, it should be a complete decal sheet.
Ever since Airfix started producing model kits, in 1952, they have always offered a free replacement parts service, which can now be done on-line, stating the kit, kit number, scale, part number and problem - the latter being a damaged decal sheet, of course - cough !
They used to enclose a request slip in all of their kits for many years, but I haven't noticed them in recent years, which was intended for the ordering of missing or broken parts.
In the case of decals, it's virtually certain that a complete sheet will be sent, as I doubt that someone is going to take the time to locate a sheet,cut the required items from it, and then post it.
Even since Airfix was taken on by Hornby Hobbies, I've never had a problem obtaining replacement parts, even for out of production kits (the latter if they still hold stocks), and despite the expected lead time they display on their web-site, parts have arrived within a couple of weeks at the most, in the majority of cases. Of course, being in 'Oz' it will probably take a little longer, but shouldn't be more than 8 weeks I would think, very possibly less, as it will be sent as an ordinary 'letter', rather than a package, being just a small decal sheet.