No problem! You can re-generate the url list (in case they add more pics) with the code below. Just change `320` to the total number of pages and paste it in the developer tools console when you're on their website.

  let urls = [];
  for(let i = 1; i <= 320; i++) {
    let text = await fetch("https://www.oldbookillustrations.com/illustrations/page/"+i).then(r => r.text());
    let matches = text.matchAll(/<img width="220" height="220" src="(.+?)-220x220\.jpg"/g);
    for(let m of matches) {
      let url = `${m[1]}.jpg`;
      urls.push(url);
    }
    console.log(i, urls.length);
  }
  console.log( urls.join("\n") );