Ed I found several sites with the Irwin Vise-Grip like in your pic. Sounds like they maybe custom built? I did find Big Horn locking drill press clamps for sale on e'bay @ $24.27 ea.free ship. Part #19630. I personally would rather have the Vise'Grip brand. I couldn't navigate the Irwin web site with my phone, maybe you could contact them with your pic to see if they are available?
1st pic Vise-grip- 2nd pic is of the Big Horn pair.