Where can I source official replica Premier League shirts for my sports shop? -

replica = counterfeitthere are no official replicas of anythingit is illegal to buy/sell counterfeit merchandise

Official gear is generally marketed by individual clubs. So, you could try contacting them direct. You do not see West Ham official kit in sports shops, at least in the London area, because they sell through their own outlets. Cannot say what other clubs arrangements are. Most official gear is made in China, but so are the fakes!