Do it wrong and you'll regret it. It's not as simple as people think, there's air pressure involved and the tire can absolutely release it explosively (to your detriment). I won't link to any, but you can absolutely find videos online of people getting pretty badly mangled for trying.
Better make them yourself. This kind of stuff is easily tracked back to the purchaser.
And, those may flatten it over time but not as fast as you want. Try sharpened hollow tubing, it'll let the air out without the rubber sealing around the edges. It's the reason spike strips are hollow, like straws.
Highschool tack welding 101. (:
