Source for corn cob media for case cleaning.

Pet Smart

Kay Kob litter. I paid about $15 for a LARGE bag.

I tried another brand, but the pieces were too large.

I use Dillon Case Polish with it.
 
Use the 20/40 grit. A lot less media stuck in the flash holes with this grade. Econoline and Drillspot carry the same, they both ship from Grainger. It's a big bag, share with your friends.
 
Just ordered a #40 bag of the 20/40 from Zoro. Found a $5.00 off coupon online. Showed up to my door in 3 days via Speedy Delivery. 40 lbs. is a lot of media - approx. 2 - 5 gallon pails full. Make sure you have a storage solution or someone to split the order with, cause it will last you many years. It shows up in a big brown bag, shipped inside a cardboard box. As with most shipping around here, the box was beat to shit, but for the most part the bag of media was intact. Will also echo the comment above - the 20/40 is small enough that it won't be a problem in flash holes.
 
+1 on lizard litter from the pet store, it is so fine that it never gets stuck in the flashholes. Thats the reason I gave up on corn. Add some nu-finish or the finish of your choice and bling.