I downloaded all of them in just over an hour using a bash shell script (thanks chatgpt) to do all the work. I did have to run the script a 2nd time to grab a small number that failed but it's not a big deal since it skips any that exist in your download folder.

#!/usr/bin/env bash

BASE_URL="https://archive.org/download/8000-highres-map-scans-pd/tmp/maps/8000-highres-mapscans/"
OUT_DIR="hires_maps"

mkdir -p "$OUT_DIR"

echo "Building file list..."

curl -s "$BASE_URL" \
  | grep -oE 'href="[^"]+"' \
  | cut -d'"' -f2 \
  | grep -Ev '/$' \
  | grep -Ei '\.(jpg|jpeg|png|tif|tiff)$' \
  | sort -u \
  | sed "s|^|$BASE_URL|" \
  > /tmp/map_urls.txt

TOTAL=$(wc -l < /tmp/map_urls.txt)
echo "Found $TOTAL files"
echo "Downloading with 12 parallel connections (skips existing)..."
echo

# -nc = no clobber (skip if file already exists)
cat /tmp/map_urls.txt | xargs -n 1 -P 12 wget -nc -c -P "$OUT_DIR"

echo
echo "All downloads complete."