Really cheap! No wonder they sold out. Probably resellers bought them all and seem them on EBay and Amazon with huge markup. Even shipping is outrageous. Must be using a private jet to deliver to you...
If they are that perfect for you I would take out a second mortgage to buy all That's available from these places and see if they can price match Umarexusa if you commit to buying every single last tin they have left.
Don't know about discontinued, but Umarex did just have them discounted to $6.99 a tin because I bought a couple, along with the 4.48 head size versions.
You might try Field Supply but they're the same place as Wing Supply and show them in stock: