Can they get you a picture of the topper? There are many different kinds of Celtic knots.
It's likely the Trinity pattern - google Celtic Trinity cake toppers and you'll see a few. It's triangular-shaped. Global Sugar Art carries some Celtic patchwork cutters.
I've done Celtic cakes in the past, and I Google "Celtic knots" and lots of pages come up. I print out the ones I like, enlarge them if necessary, and transfer them onto my cakes. In my photos here, there's a competition wedding cake of an Irish theme with knotwork on the top of one of the tiers, and on my website there's another knotwork cake here:
http://www.cakedalaska.com/Caked_Alaska/St_Pats.html
Deanna
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