If you want the standard Dulux match for Dulux Heritage Waxed Khaki, look no further than Dulux Mouse Tail. It comes in at a measured ΔE of 0 from the original — that's not "close", that's the same colour by another name. Anything under ΔE 1 is imperceptible to the eye, so you genuinely won't be able to tell the two apart once they're on the wall.
Mouse Tail sits at an LRV of 21.3, so it's a properly muted, mid-depth khaki-green — the kind of grounded, earthy tone that does cracking work in a hallway, a study, or as a moody half-height panelling colour. At that LRV it'll read soft and warm in good light and pull noticeably greener and more shadowy in a north-facing room, so test it where it's actually going.
The runner-up is Dulux Weathered Penny at ΔE 2.6 (LRV 22). That's still a very respectable match and you'd struggle to fault it side by side, but it's a touch off the original where Mouse Tail is bang on. There's no reason to settle for the runner-up here when the exact hit exists in the same range.
The obvious "but why bother" question: the Heritage line and standard Dulux are different paints, not just different labels. Dulux Heritage has a flatter, chalkier finish and richer pigment load — it's the more refined product. If you loved Waxed Khaki specifically for that velvety Heritage matt look, dropping to standard Dulux Mouse Tail gives you the colour but not quite the same depth of finish. For a budget job or a high-traffic surface where you want Dulux's tougher standard emulsions, Mouse Tail is the sensible swap.
Practical tip: buy a tester of Mouse Tail and brush two coats onto lining paper, then prop it against your Waxed Khaki reference in daylight and lamplight before you commit a full tin.