gistfile1.php

<?php

function getCMSFields() {
	$fields = parent::getCMSFields();

	/** @var DropdownField $featuredProduct */
	$featuredProduct = $fields->fieldByName('Root.Main.FeaturedProductID');
	
	$country = $this->Code;

	$list = Product::get()->filterByCallback(function (Product $product) use ($country) {
		if ($product->AllCountries) {
			return true;
		}
		if ($product->getManyManyComponents('IncludedCountries', "\"Code\" = '$country'")->Count()) {
			return true;
		}
		if ($product->getManyManyComponents('ExcludedCountries', "\"Code\" = '$country'")->Count()) {
			return false;
		}
		return true;
	})->map();

	$featuredProduct->setSource($list);

	return $fields;
}