The CrappieKiller has the best (most durable) one I've seen.
http://www.thecrappiekiller.com/killer_stuff.html
I bought one a few years ago and it is made of steel and will withstand anything. I've wasted a lot of money on cheaper versions made of aluminum, but I overtightened those and stripped them out.
If you are handy with a welder than one could probably make one fairly simple. All you need is some angle iron, 4 clamp on style rod holders, a threaded galvanized steel plumbing pipe, and a base to screw it in.
I am sure you could cut your angle iron to the desired length to fit 6 pole holders on it and/or you could always ask the "killer" if he can custom make one with 6.