I don't think they make a center to match that speaker, we get questions like this often, a lot of them older full range speakers were made for stereo playback and the speaker companies didn't make center channels with matching timbre {or centers at all at that time}. You have a few options you can find a single speaker and use that {not normally an option since they are large}, you can find a single speaker and make a center using its tweeter and mid driver with an enclosure with xover from somewhere like PE, you can find a center that will "work" start with something cheap like the pioneer aj center, and see if it sounds good, or run phantom with no center {if you have to keep the kenwoods this is what I would do...}
good luck, another good option is starting over, for a couple hundred dollars you can get a nice set of towers with a matching center and sell the kenwoods...