Positioning adverbs is a complex affair. There are some rules of thumb, but for many adverbs, it is quite acceptable to place it before or after the verb. In this case, I think either way is acceptable, though I would probably find the former more natural, i.e.


  The word rarely turns up outside of those contexts.


but the following is also acceptable, if a bit less natural:


  The word turns up rarely outside of those contexts.


Two side notes: a) you want those (the plural of that), since contexts is plural, b) of is required in both cases here, as it belongs with the word outside.

Should an adverb go before or after a verb?
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