Most d&d podcasts and shows get a bunch of free stuff that they feature (dice, minis, dice towers, stuffed animals, drawings of their characters, etc).
I doubt they buy things that someone wants to sell them.
You probably have to choose: do you want to sell it, or do you want to see it featured?
If the latter, then probably send a letter with some pictures, asking if they would feature it if you had it shipped, to whoever you want (most shows and podcasts advertise a PO Box or some such). If they answer such things on their show, chances are they'll give you a shout out and let you know on an episode. If they say yes, then you ship it to them, and that's... It.
