Wait, I'm confused. Are the discs too small for the bindings? As in they shift around when mounted? Or are you talking about the holes being off when trying to mount onto a Burton 3D board (this is Burton's 3 hole pattern)?
If it is a mounting issue with the three hole pattern, then you need conversion discs made specifically for Burton boards. Contact K2 and ask how you can obtain some.
OK makes sense now. i think what he's saying is that the plates that come with K2 bindings are not drilled at the right spots for Burton's weird triangle inserts. You can sometimes make them fit, but sometimes not.
In that case, do what Leo says: contact K2.
Or, he's trying to use burton plates or retro discs on the K2 bindings, which probably won't fit. In that case, contact K2, also