'77 KZ650 Tire Help Needed!

Hello fellow Kawasaki riders,

I have a 1977 kz650 that needs a new front tire. I just put a new 4.5x18 6PR Cheng Shin dual sport on the back and it looks pretty badass, but I can't seem to find a matching dual sport for the front with a 19" rim. Stock had a 3.25x19 aka 100/90-19 on the front. So my questions are..
Where might I find the front tire I'm looking for?
Any tips/suggestions on intertubes for this bike?
Any other knowledge your willing to impart on this new rider is greatly appreciated!
Thank you!!