Like Anthony said, we have used lathes and mill knees in the past to hex broach. Neither are recommended.
We've spent the last few years scouring Craigslist and found a 5 ton/8 ton compound arbor press similar to this:
http://www.machine-recycling.com/Sep...bor-press.php6
The travel is plenty and the press is very rigid/square. As a bonus, I'm pretty sure the tool will outlive any of us on the team
If you spend long enough looking, you can find a good deal on one. We got ours for $550.
-Mike