i've got the Tactical Tailor harness already mentioned, and i also like it, but as an addition to my MAV from the same company.
i've also got these, which i have used several times to convert large fanny packs and messenger bags with - the sternum, strap makes these really nice when the buckle on the belt of your pack is undone.
http://www.blackhawk.com/product/Load-Bearing-SuspendersHarness,37,2.htm
you can put two or more bungie loops on the belt grabbers on them, for a shock absorbing multi-point harness.
........
that all said - have you seen RIBZ...?
i've been using these lightweight altrernatives to heavier packs and they are wonderful. i even dove in mine.
http://www.ribzwear.com/
i even dove in mine. i reckon they are tough enough. they are full of rocks here.
RIBZ are good little lightweight, cheap LBE, especially when added to a datpack and such for an extended carry.
when you call RIBZ - you usually talk straight to brother ray, the owner - tell him vec sent ya, i guilt him into buying me beers.

:thumbup:
HTH.
vec