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Contrary to your above statement, I think it would be difficult (if not impossible) to show that the MACAIRA was even primarily a military instrument.
The MACAIRA can be used as an instrument of war. Just because the RHOMPHAÍAIS is longer than the MACAIRA does not mean it was not used for battle (i.e. Matt 26:47; Mark 14:43; Luke 21:24, 22:49; Acts 16:27; Rev 6:4; and in the Sept—Gen 34:25; Jud 3:16). In actuality it was the weapon of choice of assassins in that era. A.T. Robertson (Robertson's Word Pictures) states, “Buy a sword (Grk: agorasatoo, Strongs: 59) (Grk: machairan, Strongs: 3162). This is for defence clearly.”

Liddell and Scott's Greek-English Lexicon, states;

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a large knife or dirk, worn by the heroes of the Iliad next the sword-sheath, Il.: generally, a knife for cutting up meat, (Herodotus in Attic Greek) or, 2. as a weapon, a short sword or dagger (Herodotus), etc.: a sabre or bent sword, opp. to the straight sword, (Xenophon.) or 3. a kind of rasor, with the rasors single blade, opp. to scissars, (Aristophanes)

The Analytical Lexicon of the Greek New Testament, states;

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originally a large knife for killing and cutting up; in the NT sword, saber; literally, as a curved weapon for close combat (small) sword, dagger (JN 18.11); figuratively, as a symbol of violent death (RO 8.35), of hostility (MT 10.34), of the power of life and death (RO 13.4); metaphorically, for the penetrating power of words spoken by God (EP 6.17)

As Edmond Clowney once remarked;

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Disciples may claim the protection of magistrates, and indeed carry swords for defense (Luke 22:35–38); but at the risk of denying the nature of the kingdom they may not use the sword in an effort to bring it in. (Westminster Theological Seminary. (Westminster Theological Journal, Volume 31, Vol. 31, Page 55, Westminster Theological Seminary, 1969; 2002.)

Reformed and Always Reforming,