For a Dutch, a small or medium cat harness should fit. The H style one is best. Avoid the rope and figure 8 harnesses as they can choke a rabbit.
Check smaller, local stores. They tend to have a better selection and better prices. than the big box pet stores. Stores like Walmart or Target could also be good if they have the right harness.
See if you can bring your rabbit with you to try on harnesses. Most pet store do allow you to bring pets in. Just make sure you have him in a carrier for safety since you don't have a harness yet.
For the leash, many harnesses come with a 4ft leash. 4ft is too short to really let your rabbit roam. A 6-8ft leash would be better, you can use 2 4ft leashes connected together. Avoid retractable leashes as a rabbit can get tangled, the handle can hurt a rabbit if you let go and they have constant tension on the harness.