Well I had a Custom Knives plugin on my server for about a month, the uniqueness was nice while it lasted i'll post my plugin here. I'd advise someone to re-code it later when this interface when someone has time, as it's pretty sloppy coding since it was only running on my servers and didn't plan to share it. You can also use the models here in this plugin with francisco's, I got them off gamebanana but had to fix them, I could fix some more models here when I have more spare time. Oh it also uses clientprefs to save their selection and shows a knife menu on first join.
The command is !ck or !customknife, I was too paranoid to use !knife in fear of valve blacklisting
Here's a small youtube video, but this was old and doesn't have the 2 newer knives