SKU-level data are idealtypically two years of purchases summarized monthly. An often overlooked element of the data is promotion history and results. We also want to know what stores comprise the local competition for our customer.
Distributors will usually agree to share data with you once you explain how you're going to use it to plan more effective sales calls. There are also third parties who can act on your behalf in collecting the data.
Start simply, using a program like Excel to create spreadsheets for your top 10 accounts, limiting history to the last few months. There are many services, including some firms that work exclusively in the petfood industry.
Do your homework by gathering and analyzing the historical data, establish specific goals based on the data and present your well-supported recommendations to your customer.