Tell them your buddy works on a farm and asked you to get them for him. If they want to know what he needs 'em for, just say "I'm not sure, I think he uses the to haul feed, or manure, or something". I could pull that one off flawlessly.
Or use a similar story, about some guy you work with. The beauty of it, is that you don't need to tell them what they're being used for, and yet, it won't sound like your hiding anything.