Scraper For Large Retail Site

I need a software scraper that will scrape a large retail site (barnes & Noble) to pull keywords that shoppers use to search the retail site. The software needs to export results into an excel and or text file. User will input keyword and software will search retailer site and return all similar keywords results used on the retailer site and ability to sort keyword results by most search keyword to least searched. You need to pm me and I will let you know which site to scrape