I bought a pair of Stabilus SG371009 Lift Support Gas Struts from
https://www.liftsupportsdepot.com for $18 each. Fyi, Stabilus is the same name brand as my original OEM Infiniti hood stays. The new Stabilus SG371009 struts have specs (230N strength, stroke, and lengths) identical to the originals, and fit perfectly on my 2011 M56. Nice to have a car hood that stays up on its own, once again.
Strange that Infiniti has 2 different part numbers (65470-1MA0A for RHS) and (65471-1MA0A for LHS) printed on them, even though they are otherwise physically identical & interchangeable parts, and of course way more expensive ($60 each) at the Infiniti dealership.