If the condition of your volume II isn't that great, you might just want to buy the cheapest volume I that abebooks has. The binding may or may not match with the one you have, it may even be shorter or taller, but you'll still have the complete work. Just a thought.
I wish I had had the internet when I was a fifteen year old book collector. It sure would have made things easier! Flea markets and antique stores were hit and miss for cool old books that weren't overpriced.