For GB&I, other than the Clubs already mentioned, I suggest Saunton with the East and the West course. I reckon you could probably include Formby as well, although the second 18 is under the title of the affiliated Formby Ladies. St Enodoc has a second 18 called the Holywell. Frilford Heath has three 18-hole courses, the Red, the Green and the Blue. The underrated Minchinhampton has the Cherrington and the Avening plus the affiliated 18-holes at Minchinhampton Old a couple of miles up the road.
Plus, there are many top private clubs with one big strong championship course and another 18-hole course, but of a lower standard. In Scotland Royal Dornoch with the Struie, Royal Aberdeen with the Silverburn are examples of this category.
In Ireland there's Royal County Down with the Annesley. Portstewart has two or is it now even three (?) 18's. Ballybunnion has the Cashen.
All of the above may not be 'top 36-hole' but even if one of the courses at a location is superior and one lessor, IMO they are still worthy of inclusion.
All the best