Are you talking about a vest that has an integral knife sheath? If so, My Israeli Ephod vest has this. It is one of the best thought-out vest designs that isn't modular. It has a large knife sheath built in under the buttpack that carries the knife horizontally. It is easily accessible but a pain in the ass to resheath without the help of a buddy. I never carried my bayonet (as there was not much use for it in my units mission profile), but I did purchase and carry a USMC Kbar Spec Plus. The neat thing about the mag pouches on the Israeli vests is that they are sewn to the vest on the sides and not the bottm, so that long items like knives can be slipped behind the pouches to create a layering of gear. I slipped the sheath back there and applied liberal amounts of 100 mile per hour tape to secure it. The knife handle was then always upwards, easily grabable and easily resheathed.
If this doesn't do it for you, HSGI's subloads have a spot for mounting sheaths behind the compartments.