Can I make a product available to just SOME people?

Yes!

  1. Edit the Product (or Lesson or Course)
  2. Un-check "Available for Purchase" (Product Inventory & Shipping tab, or the first tab for Lessons and Courses)
  3. Check "Still allow visitors to view and purchase if they have a direct link"
  4. Click the "Public View " link (upper-right)
  5. Copy the URL of that page and send it to whoever you want to be able to buy

This effectively keeps the product from being found while searching or browsing, but someone with the direct link can still buy.