Most of the large log ends available in my area of Texas is either oak, pecan or hackberry, all of which are relatively hard, resulting in lots of no sticks. Pine is fairly available due to a massive wildfire near Bastrop Tx a couple of years ago that killed thousands of pines, but getting access to them is problematic.
A knife throwing organization, the International Knife Throwing Hall of Fame was running into the same difficulty - no decent target butt log ends available in quantity.
Last year (2013), they came up with an "Official Target", made using 2 x 4s screwed together
If you go to the following link, the the 6th video down shows how to make the targets.
http://www.ikthof.com/Videos.html
They can be made with the following tools - circular saw, drill with 1 1/8" bit and a screw driving bit, screws, pencil, straight edge. Material are 6 2x4s, 1 2x6, a 2ft x 2ft piece of 1/2 plywood, 12 3" screws and 102 1-5/8" screws.
I have a well equipped shop available to me, with a good chop saw so I can crank one out in about 1.5 hours. If I wasn't such a picky person, I could make one in about an hour, but I pre-drill pilot holes for all the screws to reduce splintering, so that adds about a half-hour. That's also with having made several and making up a check list to go by, which speeds up the process.
These targets provide a 20" x 20" area of end-grain target. I have also made them using 9 5.5" long pieces of 6" x 6". This gives me an end-grain target area about 17" x 17" that I use for ax/hatchet throwing. 6x6s are a little harder to cut, more expensive, but way faster to assemble.