The only HBB bottom-only meshes by montoto_sk which I have are these (both from January 2008):

http://www.insimenator.org/index.php/topic,70669.0.html
(best chance)

http://www.insimenator.org/index.php/topic,70303.0.html
(not likely since it is army boots with the pants tucked into boots)

The link for the mesh seems to go straight to an attachment, but uses the old link system, so it's not possible to tell which item it's referring to.

I suggest you look through the HBB section for similar meshes, and try them out ingame.
http://www.insimenator.org/index.php/board,499.0.html

There are some mesh archives if you scroll down here as well - not sure if any of them have HBB meshes:
http://www.insimenator.org/index.php/board,57.0.html