There are no conversion kits, though one could do it themselves. I thought of making one out of an old lpeg MP5A5 I used to have, but I figured the modification wouldn't look nearly as cool as if I had purchased a real MP5K.
As for the rails, you may be able to buy a new hand guard with rails on it. You wont get the shortened length like an MP5K, but still the rails.
What you can do, is get a shorter barrel, designed for an MP5K, and replace it. Find a new place to put the battery, and the rest is cosmetic work.
Bioniclebert is a moderator.