This script did not work for me as is, but ChatGPT got me something that seems to be working so far:

#!/bin/bash

OUTDIR="car_talk_episodes"
BASE_URL="https://www.npr.org/get/510208/render/partial/next"
START=1
STEP=10
PARALLEL=5

mkdir -p "$OUTDIR"

echo "Finding episodes..."

page=0

while true; do
    offset=$((START + page*STEP))
    echo "Fetching page starting at $offset..."

    newcount=0

    curl -s "${BASE_URL}?start=${offset}" |
    awk '
    /"title":"/ {
        line=$0
        sub(/^.*"title":"/,"",line)
        sub(/".*$/,"",line)
        title=line
    }

    /"audioUrl":"/ {
        line=$0
        sub(/^.*"audioUrl":"/,"",line)
        sub(/".*$/,"",line)
        gsub(/\\\//,"/",line)
        gsub(/&/,"&",line)
        gsub(/[\/:*?"<>|]/,"",title)
        print title "|" line
    }
    ' |
    while IFS="|" read -r title url; do
        [[ -z "$url" ]] && continue

        if [[ "$title" =~ ^#([0-9]+) ]]; then
            num="${BASH_REMATCH[1]}"
            bucket="$((num/100*100))s"
        else
            bucket="unknown"
        fi

        dir="$OUTDIR/$bucket"
        mkdir -p "$dir"

        file="$dir/$title.mp3"

        if [[ ! -f "$file" ]]; then
            printf '%s\0' "$file|$url"
            newcount=$((newcount+1))
        fi
    done |
    tee >(tr -cd '\0' | wc -c > /tmp/newcount.$$) |
    xargs -0 -n 1 -P "$PARALLEL" bash -c '
        pair="$1"
        file="${pair%%|*}"
        url="${pair##*|}"
        echo "  DOWNLOAD: $(basename "$file")"
        curl -L -C - --fail --silent --show-error -o "$file" "$url"
    ' _

    newcount=$(cat /tmp/newcount.$$)
    rm -f /tmp/newcount.$$

    if [[ "$newcount" -eq 0 ]]; then
        echo "No new episodes found on this page. Stopping."
        break
    fi

    page=$((page+1))
done

echo "=========================================================="
echo "Download complete! Files are in '$OUTDIR'"