Tire suggestion for rear of 78 KZ650-B2

My recently purchased 78 KZ650 needs a new rear tire. The front tire is new (by previous owner) and its a Michelin Commander II. The problems is they don't make a matching Michelin Commander II in a 120/90-18 for the rear. So my options are to buy another make/model tire for the rear. Or replace both with new tires. I hate to replace the front since its new. I can get a "Michelin Pilot Activ" in the right size for the rear but it's not the same model as the front. What would you do. I'm not a hard rider and mainly ride around town for short distances. Thanks for any thoughts.
Dale - AZ

I would replace the rear tire with a Pirelli 120/90 V 18 Sport Demon or replace both tires using a Pirelli 100/90 V19 Sport Demon on the front. I've been using Sport Demons on my 1977 KZ650-C1 since 2009 (about 13,000 miles - I'm on my second set) and I really like them a lot. Ed