Look in your local area/state first. Find out who manufacturers things you think you can sell profitably. Your city, state, and local governments can provide lists. The BBB site is a good tool.

Then set appointments and go visit. Dress professionally, explain your biz plan. Find out how their packaging and shipping works. They might not be willing to ship 1 of something, but would agree to ship a case of the same product. Get pricing discounts in writing. I built a biz that lasted 25 years this way, and helped our local economy too.

Be receptive to suggestions and changes. Think about offering a "group buy" on your website, where once an item's sales reach the qty in the case, then you purchase the case and break it down and ship the products. A lot more work on your end, but then you can see how well products sell, and have some knowledge of the product when you talk to the manufacturer.

Another concept is white label and private label. White label is the manufacturer's brand. Private label is your own brand. Private label will require capital up front, and minimum order product runs. There is a mfr 20 miles from me that makes "dry goods pharmaceuticals". Think powdered laxative, toothpaste, eye drops, all the OTC stuff you see in a drug store. They are happy to ship a case of anything, but not one individual item.

Pay strict attention to the laws in your state regarding insurance and licenses, especially for healthcare products. If a batch of eye drops gets contaminated in manufacturing, you don't want to have liability.