I like the idea of havving an ally but i dont think that colonial will be an option. Why? If im correct then colonials are lost thier home to gallia and now they are one of the three exiles ( council, colonials, kusari exiles). It will be better that if they allied with bretornia with other exiles.
However i think the best feasble will be corsairs. Sairs have good player base. Enemy of bretornia and currently trying to set a foot hold on chembridge. As bretornia is already friendly with oc and molly against sair and gallia this senario is feasble too.
The only problem is sairs are pirates and dab will never do allience with pirates i think. But if we back track in the case of sleeper ships then we can at least we have a point. They were like the houses each with thier sleeper ships. The others have taken good resourceful sectors and leaving the hispanics no choice but to land on distant land. They are not pirate by origin.. They are forced to do this for leaving. Allying with such clans who similarly betrayed by sirius people wont be bad move i think.