The Zimbabwe dollar is not an official currency, so as such is is not pegged against other currencies except for the US$. You could possibly find a vendor at the border who would exchange your Kwacha for Zim bond notes but he would first exchange into USD and then into Zim bond notes.
My experience of this is that they will give you a terrible exchange rate and you will get ripped off. Best advice is to bring USD which you are able to use here freely and pay for most things with a credit card.