Green Smoke is one of those F&B colours people fall hard for — a deep, dusky blue-green that sits beautifully in low light and reads almost grey on a north wall. The good news is you don't have to pay F&B money to get it.
The pick of the bunch is Crown Fern Canopy (LRV 18.6). It lands at ΔE 1.3 from the original — inside the "very close" band, only a whisker off imperceptible. Put the two side by side and you'd struggle to call it. Crown's trade emulsion is a genuinely good paint, and you'll save a fair bit per tin.
If you'd rather a modern water-based formula that dries fast and lays off cleanly, COAT Retrograde (LRV 18.6) is right there at ΔE 1.5 — still a very close match. COAT's eggshell and emulsion are low-VOC and recoatable in a couple of hours, which is handy if you're decorating around a weekend.
I'd steer you away from Dulux Mouse Tail (LRV 21.3) for this one. At ΔE 4 it's in the same family but noticeably lighter and a touch greyer — close, but you'd see it next to a Green Smoke door or skirting. If it's the only one you can lay hands on locally it's a serviceable approximation, but it isn't a true dupe.
One thing to flag, mate: with deep greens like this, the finish and sheen affect the read as much as the colour. A flat matt will swallow the depth and look almost charcoal in shade; an eggshell or modern emulsion holds the green-blue better. Whichever you choose, get a proper sample pot, paint two coats on a bit of lining paper and move it round the room over a day. North light, evening lamps — it shifts. At ΔE 1.3 Fern Canopy will behave just like Green Smoke would, so once it's up you can stop fretting and crack on.