I'm looking for ideas/suggestions regarding any rig available to allow inverted carry of a boot knife on the leg when wearing
dress or other non-boot shoes.

This would allow the knife to be quickly deployed by just pulling the knife downward. A secure retention system in the sheath would certainly be a necessity.

Guess I could make one using one of the more elaborate ankle holsters available which has a calf strap, but I would prefer one mfg for that purpose.

Appreciate your thoughts and perspective.

Southampton

There's nothing quick about an ankle holster, whether it's for a knife or a handgun. In order to draw the knife with a downward motion, it seems as if the would place the user more off-balance than if the knife faced up, which would allow for a more balanced stance. I suppose you could use a KA-BAR TDI in an inverted position.

Tomar's KA-BAR Knives- TDI Law Enforcement Tactical Defense Ankle Knives

There aren't any rigs for knife carry that beat a rig for gun carry, so don't be the one who has the epitaph "He brought a knife to a gun fight."

Take a look at the Tekna Dive Knife. It has a sheath that retains the knife in the sheath through a hole in the bottom of the handle. The retention of the knife in the sheath is GREAT, as it requires the lifting of the tab that fits into the bottom hole in the handle before the knife is released from the sheath. The blade is only 3.5" but can be worn on the belt, forearm and ankle. I've worn mine on all of the above locations and have never had a second thought about it coming loose. If you plan on wearing it on your belt or ankle be aware that Tekna produced three versions of the sheath, one with a "Spring Wire" that fits behind the belt only, one with "Velcro" strips that fit on the forearm and leg only and one with the sheath built onto an O2/Compass guage for SCUBA diving, after all this is a diving knife, it just happens to be double edged, SS and has a needle point tip.

Class III

Edit: Tekna has not produced this knife in about 20 years. Good luck finding one on the used market as they are highly sought after items. NIB generally go for $300 plus.