Having owned one in the past, I am sure they were only made in bilge keel versions. Reason being that the moulding included encapsulated bilge keels in a one piece hull mould - and I have also never heard or seen a fin keel version.
Yes, Colvic certainly made at least one fin keel version of the 26ft sailor. There used to be one moored on the Exe.
I expressed surprise when I saw it laid up at Retreat Yard, Topsham some years ago as I had never seen a fin keel version advertised by Colvic. The owner did not claim it to be unique, but said it was rare.