I've had a quick scan through what books I have, and haven't been able to find anything that closely matches what you're talking about.
Plenty of La Tene designs that have concentric circles but not on their own, rather as part of a more complex design.

Of course, the EB team have access to material I don't and it's such a simple design that I would expect it to turn up everywhere.

The clearest examples that I did find were in fact Germanic/Nordic. A beautiful spearhead found at Vimose in Denmark (5th century AD) on p16 of my copy of Seamus Hearney's translation of Beowulf. (can't find a google picture sorry) has concentric circles inlaid with silver on the black iron of the spear blades.