I got 'em from amazon, the tube has roughly 40 death nuts for $25, the challenge only has a couple of them and then less spicy ones for $19 so I think the tube is a better value...

https://www.amazon.com/Tube-Terror-Challenge-verified-Carolina/dp/B07WZBJCLC/ref=sr_1_3?crid=2PF8W463OTE9R&dchild=1&keywords=death+nut&qid=1611755556&sprefix=death+nut%2Caps%2C223&sr=8-3