T'Ong Nebula: Mk II and Mk IV samples
D'kel Star Cluster: Mk IV and mk VI samples
Eridon Nebula: Mk VI and Mk VIII samples
Azlesa Expanse: Mk VIII and Mk X samples
Azlesa Expanse (Elite): Mk XI samples
Haven't been able to assess all fed nebulas yet (to be precise just have been in delta volanis).
Another thing that makes klingon data gathering a tad more difficult is that there are far more players allowed in each cluster before a new instance get opened, fed clusters don't allow more than five players in one instance while I've seen up to eighteen concurrent players in a klingon nebula (I assume that it allows up to 25 players in a klingon cluster same as 'normal' sectors).