The Armorer subclass of Artificer has the Arcane Armorer feature which gives the option for:
Thunder Gauntlets. Each of the armor's gauntlets counts as a simple melee weapon while you aren't holding anything in it, and it deals 1d8 thunder damage on a hit.
However not every type of armor includes gauntlets. The Breastplate for example makes no mention of gauntlets in its description.
If your armor does not include gauntlets and you use the guardian form for your Arcane Armor would you create your own gauntlets or would you be unable to use Thunder Gauntlets?