Hi Jules, thanks for the question, sadly there is not a great choice in many catalogues or stores.
Also varieties mentioned in that 2006 article such as Aruba, Moroccan and Redina are now rarely seen for sale. Not that they are suddenly "no good", more I think a question of seed houses wanting something new and ‘more interesting’, every year!
Since that article was written, I have tried many more varieties and found that most of them are good, depending what you want. My current favourite leaf lettuce varieties, which should be available just from googling, are Freckles, Rosemoor, Chartwell (all cos), Maravilla di Verano & Grenoble Red (batavian), Navara (red oakleaf), Bergamo (yellow Lollo Biondi) and Amorina, which is pink and frilly.
Any of Mr Fothergills, EW King, Stormy Hall Seeds, Marshalls, Seeds of Italy, Real Seeds and Simply Vegetables are worth a look.