KZ400 Tires

I need tires for a '76 KZ400 that I recently got running again. The current tires are 3.25x18 and 3.50s18 and I'm having trouble finding replacements.

I'm looking for high mileage and a decent price, and I'm not overly concerned about grip or feel as it's not my primary bike. What fits? What do you all recommend? I searched briefly and didn't find anything.

try 90-90-18 and 100-90-18

try j.c. whitney or redlinecycle.com,,,they may have them