Are there any knotwork designs uniquely associated with specific Celtic countries?

No, I am not aware of any Celtic knotwork or interlace design being associated more with one Celtic people group than with any other. I'll try to spare everyone a long history lesson, but here is a short version: If you go back far enough, Celtic peoples actually stretched all the way from Spain and Portugal to Asia Minor. Over the millennia, invasions & migrations eventually forced them into what is now known as the "Celtic Fringe" countries of Ireland, Scotland, Wales, the Isle of Man, Cornwall in England, Brittany in France, and Galicia in Spain. Knotwork and interlace do not appear in the earliest known art/culture of peoples identified as "Celtic." What is now recognized as Celtic-style knotwork and interlace arose centuries later through a combination of early Celtic design, Germanic animal interlace, and Mediterranean influences brought by Christianity. From about the 5th or 6th century C.E. onward (peaking between 700 and 900 C.E.); we begin to find fabulous examples of ...  more