Here's one from one of OUR vendors http://www.penturners.org/forum/showthread.php?t=43966
It's called a "Center finding square" , and you can buy one from Victor (landfilllumber) for $12.50 in the above link , and it's made of metal not cheap plastic .
We all have the same problem, here is my solution.
This post may get me kicked off the forum for its stupidity, er, simplicity, but here it goes.
I got a penny and drilled a tiny hole in the center of it. Then I place it on the end of the blank, centered, and using a small punch or nail, mark the center.
If you want to make one of these yourself, here's a hint: there is an image of Abe on the reverse of the coin in the center of the pillars – I needed a magnifying glass to see it – drill the hole right in his stomach!
My total cost of this jig was 3 cents, I didn't get the first 2 centered.
This is not the best picture, I was in a hurry to get it out here for all to laugh at.