φέρε λαβών, ἔφη, χιτῶνας μὲν τουτουσὶ τοῖς τῶν δορυφόρων ἡγεμόσι, κασᾶς δὲ τούσδε τοὺς ἐφιππίους τοῖς τῶν ἱππέων ἡγεμόσι δός, καὶ τῶν ἁρμάτων τοῖς ἡγεμόσιν ἄλλους τούσδε χιτῶνας.
does this fere go with the imperat, or does it stand by itself?
sorry, it is clear from the context that is stands by itself
I wouldn’t say it stands by itself. It’s to be taken very closely with the imperatival λαβὼν … δός. It’s an exhortative (παρακελευσματικόν) used much like ἄγε, though ancient grammarians distinguish the two.