Back on page 6 of this thread, RTR12 mentions ordering them at DigiKey but I didn't see an actual part #. With the Jan 2019 price hike by USPS, the minimum DigiKey shipping charge for First Class Mail is now over $4.
As mentioned in the post above his, I get them for about a dime a piece on eBay (free shipping from Asia). Search eBay for "2.54mm screw terminal 2 poles"