Not sure about 5.5, but I have a Rocketry Warehouse 4" fiberglass conical nose cone that fits slightly snug in a LOC 4" airframe. You can source this from Madcow Rocketry since they recently acquired RW's stuff.
Loc 5.5 tubes have an inner diameter of 5.38". I'd look at the 5.5" cones available and ask the vendor if the shoulder ID fits (if they don't know, they'll probably measure it for you because it increases the likelihood of a sale if it fits )
Good luck hunting! I was lucky to get a custom 5.5" elliptical that fits loc tubes from the stuff Mike Stoop (Madcow) got from rocketry warehouse in the buyout.