To understand Orwell's point, more context is in order. I'm leaving out most examples of Bad Writing indicators he gives which tend to be single words each.
Foreign words and expressions such as [...], individual (as noun), [...] are used to give an air of culture and elegance. Except for the useful abbreviations i. e., e. g. and etc., there is no real need for any of the hundreds of foreign phrases now current in the English language.
Bad writers, and especially scientific, political, and sociological writers, are nearly always haunted by the notion that Latin or Greek words are grander than Saxon ones, and unnecessary words like [...] constantly gain ground from their Anglo-Saxon numbers. The jargon peculiar to Marxist writing (hyena, hangman, cannibal, petty bourgeois, these gentry, lackey, flunkey, mad dog, White Guard, etc.) consists largely of words translated from Russian, German, or French; but the normal [non-Marxist Bad Writer's] way of coining a new word is to use Latin or Greek root with the appropriate affix and, where necessary, the size formation. It is often easier to make up words of this kind [...] than to think up the English words that will cover one’s meaning.
Before we drill into "these gentry", please note that Orwell is not offering "individual (as noun)" as an example set phrase consisting of three words, but as a single word with an extra qualification.
In the quoted text, Orwell is referring to, and actually pointing out, the origin of the word "gentry" from Norman French "genterie". (In contrast, the word "these" was not translated from any of Russian, German, or French, and Orwell must have been excellently aware of that fact.)
Here, Orwell is disparaging pretty much any usage of words like "hyena" (when refering to a person) or "lackey" on the basis of English having more suitable terms of Anglo-Saxon origin for the same meaning, which would be used instead, if focus was on communication and not on showing off one's rich vocabulary. For some reason he doesn't seem to be so categorical about any possible use of "gentry", and so he decided to qualify that word with some extra (example) context which he claims to be characteristic of Marxist writing and simultaneously a good example of a context in which this use of "gentry" indicates that a Bad Writer is injecting the word "gentry" for the sake of showing off Bad Writer's vocabulary only. So much for Orwell.
To switch the sides, let's google up a random usage of "these gentry" by Marx. It was by accident (of Google Search ranking) that I stumbled on the same occurrence as mentioned in the OP:
I shall aim a few necessary blows at Bastiat [...] Faucher and consorts [...] Moreover, the worthy Bastiat did not even himself make this ‘discovery’, so welcome to these gentry, but just ‘cribbed’ it, in his usual manner, from much earlier authors.
In the end, "these gentry" boils down to "aforementioned gentry" (presumably Bastiat, Faucher, and those unnamed "consorts"), but the word "these" is pointing to them not just for ante-reference, but also for some extra ridicule, in this particular, randomly chosen, sample of Marxist writing. (Marx could have said just "them" if his needs with the phrase had been just the grammatical ones.)
And "these gentry" is in no way isolated in that shade of meaning of scornfully pointing to an opponent: the entire list of words which Orwell attributes to "Marxist writing" is like that.