The LEGO Star Wars: The Force Awakens C-3PO (5002948) minifigure polybag promotion is now live at Toys R Us stores. You can get it free with purchases of $40 or more with any LEGO Star Wars purchase of $40 or more. If you have trouble finding it in stores, check with the cashier or at guest service as they might have them hidden behind the counter and give them the item number 169326.
I did a check at work to see how many are around San Diego and most stores have around 200 in stock. Depending on how nice the employees are at TRU, you may be able to purchase one separately for $3.99 each. If not, just wait until the promotion ends next week and they’ll just sell them regularly.