The 'a' changes the meaning: "I was glad to have landed in such a good company" (a [good] company = place of work, business) "I was glad to have landed in such good company" (good company = group of friendly people) "I was glad to have landed in such a good company of men/women/soldiers etc" (group of men/women/soldiers, usually together for some purpose)

No, not if you mean being in a group of people and not being alone (with friends, etc.) It has to be non-count -- "in good company". And the verb "land" sounds off with that meaning. (Still, I'd understand what you meant.) Hearing it as a countable noun makes me first think of a business/firm. "A company" can also be a theater / opera / ballet company. If you use "land" with the countable form, you'd probably "land a job with a good company."

Alex, If you want to do serious dicitionary research you need to download the Oxford English Dictionary (full version). There you will find the definition that supports your usage of company ( a group of people) as a countable noun. It is between the definition 4.a (collective) Persons casually or temporarily brought into local association, travelling companionship, etc. More loosely, with the notion of companionship obscured, ‘People such as prevent solitude or privacy’; and so applicable to a single person. Obs. exc. as referred to 5*. and the definition 6.a A body of persons combined or incorporated for some common object, or for the joint execution or performance of anything; esp. a mediæval trade guild, and hence, a corporation historically representing such, as in the London ‘City Companies’. This is the definition you are looking for 5A. 5.a A gathering of people for social intercourse or entertainment; a social party; a circle. Formerly a reunion or assembly of more public character. 1774 Chesterfield Lett. I. Advt. 14 He presumed his Son might thereby be domesticated in the best foreign companies. 1851 Helps Friends in C. I. 1, I can add little or nothing to the pleasure of any company. b.5.b (without a or pl.). Guests collectively; one or more persons invited or entertained. I know that I have definitely read "a company" in the sense that you are using it in older English literature but it does seem a bit dated , though not obsolete yet according to the Oxford. I did find a comtemporary instance of your usage on the net: Thank you for joining me on this adventure, it has been a real pleasure to stitch this piece in such a good company.