I don't know that there's any charters of that sort of thing, but who might be some plausible candidates outside the obvious? Presumably Harold Godwinson's brothers the Earls of Kent and East Anglia, Edwin the Earl of Merciaand his brother Morcar the new Earl of Northumbria. What about clergymen? Stigand? Anyone else? Are there other notable nobles that might've participated?
We only have one charter of Harold I, but the various witans of the 1060s are fairly well attested through the extensive charter record of Edward the Confessor.
There are no attestations on S1163, our sole Harold writ, although it is addressed to an abbot 'Ayllnođ' and concerns the lands of Bishop Gyso.
S1043 is a charter of Edward from 1066 conveying lands and privileges to the new Westminster Abbey. Apart from himself and Eadgiđa, his Witan on this occasion includes both archbishops, Stigand and Ealdred, his cancellarius Reinbald, the Dux Harold (Godwinson) of Wessex and his brothers Leofwine and Gyrđ, and Eadwine of Mercia, a wide array of bishops (Walter, Leofric, Willielmus, Herreman, Wulfstan, Siward, Wulfwin, Gyso (Bishop of Wells), Ælfwine, another Leofric, Ægelsius, Eadwine, and Wulfwold), a number of abbots, and six 'ministers'.
On a separate occasion (S1042), his Witan still includes Stigand, Ealdred, Harold, Gyrđ, Leofwine and Eadwine, and a similar collection of bishops, but also includes Tostig, Earl Waltheof of Northumbria, the procurators Bundi, Raulf, Esgar and Hrođbehrt (likely royal officers), the pincerna Heardyng (a member of the royal household), the cubicularius Winsi (head of the royal household), and the Princeps Brihtric, Ælfgar and Ælfstan (probably local "tribal" rulers).