First off, hi and welcome to the forums. There's a thread for introductions...so feel free to go introduce yourself!
Secondly, from the rest of your stripdown pics you appear to have a KWA PTP M9 not WE M9. That may have a slight bearing on what you need to get. Best bet would be to have a look on ebay for a pack of springs. Look for length and diameter. Just because it's an airsoft pistol doesn't make the spring terribly special. Should cost pence. Or try an engineering suppliers or maybe an RC car spares place, they use all sorts of fiddly little springs.