Alibaba is a ecommerce site dedicated to selling in bulk from countries and companies all over the world. Individual products may also be purchased but the more you buy the cheaper it is. (Shipping can also be expensive so you have to do your research for the best prices) Custom logos are also available from some suppliers if you buy over a certain amounts at cost. Always see if suppliers you want to buy from sell on amazon if purchasing individually, as it may be cheaper.
I also recommend chatting directly with suppliers instead of buying yourself from the site! Sometimes you can get deals on shipping.