A while ago I got one from my local car parts place, IIRC it was an NGK one but it didn't last a year so I got a genuine one which was way more expensive but still going strong.
I would try, cox motor parts, they have always been great sourcing parts and are genuine parts, Lings Honda was another but expensive or maybe try Jap service parts they sometimes do genuine products or aftermarket ones made in the same Japanese factories as genuine apparently.