I indeed used dnsdumpster.com. Scroll down to Host Records (A) and then use the subdomains (marked in yellow):
I used Google Chrome and Bitwarden’s browser extension. After changing the URI and saving a reload of the webpage is not necessary, but closing and re-opening the window of the extension seems to be necessary. Furthermore: Depending on the server the result might not appear instantly. Just give it some 5 to 20 seconds. This actually seems to depend on the server. The URIs I mentioned above really do provide the icons. Going through a list of host records that long as it is for Carrefour takes time and patience. It is annoying that some of their servers react that slow.