Nice and convenient for you (assuming you have a rental vehicle) is the Golden Grove Farm Shop. This butcher their own stock and have other good imported stock. I DON'T recommend their sausages if you intend slapping them on the barbeque though - we nearly set a villa on fire last March when the sausages went up in flames. The beefburgers were the best I've ever tasted though and the steaks acceptable (don't expect decent steaks by North American standards anywhere in the southern Caribbean).
The best way to find the Golden Grove is possibly via our Satellite Map. Select Tobago > Maps & Regions from the menu bar at the top of the page then click on the Satellite tab (or on the image in the centre of the page). The Golden Grove is on the default page, so after the map and markers have downloaded, switch off all the markers EXCEPT the Food Stores. The red icon for the farm is almost in the middle of the page. Hover over it for the name and click for further info. You can then switch on the villas and identify where you will be staying and zoom in to see the best route to the shop.
myTobago.info - the definitive Visitor Guide to Tobago