If anyone is selling TnT I will buy it! I buy it at 20 NBZ a piece at my shop in DeepHaven. Just do /t spawn Deephaven to get there. Then walk straight forward until you see a
GIANT TnT (Statue?) block. Thingy. At the entrance are my Firework cannons. Ignore those. Right outside the main door, I have little shops for selling TnT. If you are selling only a few use the one on the left. If you are selling a lot use the shop on the right. If there is TnT in there you are free to buy it.
Happy shopping.