This appears to be associated with Michael Foster's operation. Might be OK as a supplemental source.
https://
www.cefchannel.com/
I also ran into this website that's not exclusively focused on cefs but its a convenient source to capture institutional holders of shares. The amazing thing is that there are now so many institutions holding cefs in their ports. I can remember when no self respecting money manager would hold any cefs since they are paying another manager to run investments but that inhibition is long gone.
https://
www.holdingschannel.com/bystock/?symbol=dni