It's most likely just a Swordwind formation, hailing from Craftworld Biel Tan (who use a disproportionate number of Swordwind hosts relative to other craftworlds.)
A Swordwind (also roughly translated from the Eldar language as "leaves falling to cut") is an Eldar Warhost which features a disproportionate number of a Craftworld's Aspect Warrior shrines in its composition. Guardians are provided almost solely for vehicle crews, and the emphasis is placed on the embodiment of Khaine's aspects united. A Swordwind is often lead by a Craftworld's Avatar of Khaine, and is accompanied by The Court of the Young King-- a group of Exarchs (and their squads, sometimes) which attend the inner sanctum in which the Avatar rests.
IIRC, Alessio Calvatore did an article in WD about Biel Tan organisation and the court of the Young King about 3 years ago - certainly before the new eldar 'dex came out. Don't know if it's available online, and nor can I remeber what issue number it was... but then again all the local editions are different anyway aren't they? Oh pants... I'll try to find it, then at least you'll know the UK edition.
Anyway, it exists somewhere; not specifically Swordwind Sylvanos though, sorry.
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