I have just purchased a used Ruger 77/22 rechambered to K Hornet. Can one use neck size dies for the standard Hornet to neck size K Hornet brass? I have a fondness for the Lee Collet dies but I don't think they're made in K Hornet.

You can't do it. You could the other way i.e. use 22 K-Hornet to size 22 Hornet but not the way you want.