How can I un-seize track nuts? I bought a set of these about 18 months ago now and for a little while they continued to work as they should but then now they're seized up.

Is there anything (short of ordering another pair) I can do to release them? They're not stuck to the bike or anything like that, it's just that the grippy  bit is supposed to spin independently of the hex bit.
I would use the same techniques as used on rusted hardware. Liberally apply a penetrating oil (liquid wrench, PB Blaster, CRC Knocker Loose). Use a penetrating oil not a lubricant to break them loose. With the nuts being so small you can soak them in a small container for several days. Then hold the flange with pliers while turning the nut with a wrench.  Once it is freed up I would apply either Never-Seize or a dab of grease that will keep the water out and rust from forming.