Which size tube for my tire?

[ayelvington]

I got a sidewall cut today on a front tire that's too large for the Slime to reseal. The tire is 18x8.5-10

Apparently no one makes a tube for this tire, and the only 18" tube that I can find is for an 8" rim. (too small)

Can someone point me to a tube that will fit?

Thanks in advance!