I've got some Creed caps that I acquired over the past year and it's amazing how the caps take on the smell of whatever they were originally on.
For instance, I bought a couple of bottles of hard to find Creeds on eBay and the sellers stuck on a mismatched Creed cap just to put something on it. When I received the bottle and smelled the sprayer, I was concerned at first because the sprayer had taken on the smell of the cap (that didn't match the scent in the bottle). That was quickly remedied by one spray and leaving the cap off. But even after soaking the caps in warm water, I could still smell the original fragrance they were on.
Back to the concerns of the OP though....I can understand wanting to have a cap to make the bottle complete. If you don't find one, however, don't let your OCD interfere too much with your enjoyment because testers aren't supposed to have caps. At least, they frequently don't. And if you ever decided to sell it, you could just list it as a tester and most buyers will understand the reason it doesn't have a cap.
Green Valley is a fantastic fragrance! You were very lucky!