I have the exact opposite pref. In most of Europe ISO layout (with various country-specific accents) are standard and it can be hard to find a US (ANSI) layout (with horizontal rather than vertical Enter).

In the Netherlands, most brands seem to default US layout, but some (most notably Logitech and Apple) still default to ISO, with a thin vertical Enter. Even "International English" (Apple) or "International American" (Logitech) tends to be ISO. Fortunately Apple offers US English in their online store nowadays (but not in any physical stores). But for Logitech AFAIK it's impossible to get an ANSI US layout in Europe without importing it yourself from the US. Worst thing is, most of their marketing still shows the US layout, and many retailers have no clue about different keyboard layouts nor what they're actually selling.

Are you searching for high-end (not necessarily custom) mechanical keyboards? I think I can count on one hand the number of times I've seen a keyboard more than $100 or so that didn't support an ISO layout.

The big downside of the ISO layout is that the enter key is no longer in reach of the right hand -- you have to move away to press enter. I use enter way too much for it to be out of reach.