A replica product is a product produced to replicate the original, and it is illegal to sell because it has been made outside of the brand owner's licensing requirements.
A designer inspired product is legal to sell because it is only based on the designer's product, it does not attempt to replicate it in authentically. For example, a designer inspired Chanel handbag would not carry the Chanel brand name, would not intrude on any specific design copyright issues that were applicable that is licensed to Chanel, and so on.
Let me know if you are after the designer inspired lots, there are several suppliers that I can recommend. :)