The jockey wheels? You should have lots of options. I wouldn't worry about getting the original ones. Any 9 or 10 speed jockey wheel intended for Shimano should be fine. Ideally I'd make sure you get a set with a designated top and bottom wheel* because they are meant to be different and that is how the shifting is designed. Maybe cover yourself by asking the seller if the wheels are specifically compatible with your derailleur just in case.
Also a 10 speed rear derailleur will work with the rest of a 9 speed Shimano groupset. You should still be able to get 9 speed stuff but it might be a little harder to find and sometimes the newer stuff is cheaper because there is more of it around.
* Edit - bit of clarification - Shimano make jockey wheels, I'm sure, would have a top and bottom. I meant some 3rd party ones might not, they still might shift fine but, given the choice, I'd get ones with a top and bottom specific wheel.
Also a 10 speed rear derailleur will work with the rest of a 9 speed Shimano groupset. You should still be able to get 9 speed stuff but it might be a little harder to find and sometimes the newer stuff is cheaper because there is more of it around.
* Edit - bit of clarification - Shimano make jockey wheels, I'm sure, would have a top and bottom. I meant some 3rd party ones might not, they still might shift fine but, given the choice, I'd get ones with a top and bottom specific wheel.