Amazon Product Data Upload

We are looking for an expert in uploading Amazon product data for my sporting goods company. We are an ecommerce company that carries brands such as Asics, Adidas, Cliff Keel and Matman. The product information is already in Excel with UPC codes but I'm having a tough time successfully uploading the data into Amazon inventory. In addition, some products that are already uploaded I can't seem to find them where the should be on the Amazon Product detail page. There are about 50-75 products - most have sizes and variations which will be supplied in the Excel File we are using. Freelancer's must be expert and thorough so that products are uploaded successfully and listed properly. We expect to have additional work throughout the year as we integrate new 2012 products into our web-site and Amazon.