terrā: Was used stand-alone by Cicero here: Brundisium terrā petere ”to head towards Brindisi by land.”
marī: According to F. Calonghi, Dizionario latino-italiano, 3th ed., 1969, was used stand-alone by Cornelius Nepos with the meaning “by sea”. Unfortunately, without precise reference. However, see Cicero’s quotation below.
militiae: According to L. Castiglioni - S. Mariotti, Vocabolario della lingua latina, 4th ed., 2007, was used stand-alone by Cicero with the meaning ”in wartime”. Again, no precise reference, but see edit below.
Neither expression that you mention is fixed: you get very many examples of variations like militiae domique, et mari et terra, mari terraque, aut mari aut terra.
Technically, neither terrā nor marī are locatives. They are regular ablatives: terra's locative, if it existed, should be terrae; mare does have an ablative mare used by Lucretius, Ovidius and other poets but you get zillions of examples of in mari, a mari, de mari, and there is no doubt about which form is the preferred one. So terrā and marī belong in the list of locative ablatives, together with dextrā, laevā (on the right, left), speciē (under the pretext), linguā (in the language) and so on. They are closely related to ablatives of manner, and in fact they seem not to refer to a location (at land, at sea) but to a manner of displacement (by land, by sea). Locatives like domī or rurī are never used together with adjectives (domī meae et sim. being an exception); on the contrary, Cicero writes for instance here:: cum aut hieme aut referto praedonum mari navigaret (sailing either in winter or through a pirate-infested sea) with ablatives without preposition.
Finally, I would like to point out that it is possible that the meaning of terrā marīque evolved from the simple coordinated use of both components. I have the example of Italian, where per mare e per terra has become just an imaginative way of saying “everywhere” (much like “over land and sea”), while per terra alone has become “on the floor” and in the modern language you have to say via terra to get the original meaning of “by land”. Therefore I would suggest that a precise analysis be done before translating such variations as et mari et terra, which might have the original meaning of “both by sea and by land”, in contrast to terra marique which might have a “diluted” meaning. Each occurrence might be different.
Edit:
Lewis and Short say:
Gen. militiae, in military service, or on a campaign, in the field; freq. in phrase: domi militiaeque, ... —Also without domi, Cic. Leg. 3, 3, 6; Sall. J. 84, 2; Tac. H. 2, 5.—
but Cicero’s and Tacitus’ occurrences are not convincing at all, and I hope that Castiglioni-Mariotti’s ghost reference is not one of them. OTOH, Sall. Jug. 84 is peculiar, showing a locative contrasting with an ablative of means: plerosque militiae, paucos fama cognitos, i.e. “most [of them] known [to him] by actual service, some few only by report”.
