If you want the look of Paint & Paper Library Stable Green without the premium price tag, Dulux Palm Night is the one, mate. At ΔE 1.3 from the original it's an effectively imperceptible difference to the eye — anything under 1 is invisible, and under 2.5 is very close, so 1.3 sits comfortably in "you'd never know" territory. With an LRV of 4.9 it's a deep, inky green that holds its character in low light, same as the original.
If you'd rather stay a touch boutique but still save, COAT Brewer (LRV 7.2, ΔE 3.9) is a slightly lighter, greener take. It's not as faithful a match — at 3.9 you'll spot the difference side by side — but it's a lovely colour in its own right and COAT's matt emulsion is genuinely good stuff. Crown Racing Green (LRV 6.2, ΔE 3.3) sits in between on accuracy and is the most wallet-friendly of the trio.
The "but what about the finish" question always comes up here. Stable Green earns part of its reputation from P&PL's chalky, deep pigmentation — so the honest answer is that a ΔE figure tells you about the colour, not the texture or the way the paint flattens out on the wall. Dulux Palm Night in their Heritage or a good flat matt will get you very, very close, but if you're doing a feature room where the depth really matters, buy a tester of Palm Night first and live with it for a couple of days.
Practical advice: deep greens like this drink up light and show roller marks, so apply two even coats over a grey or tinted primer rather than white — it stops that patchy, see-through look on the first coat. And keep a wet edge; dark emulsions are less forgiving than pale ones.