Where can I find classic tires for my old model T online?

Lucas tires can help with that. Here is some info from them on those tires www.lucasclassictires.com/MODELT032009.pdf

Lang’s Old Car Parts (http://www.modeltford.com/c/741152450/i/page1.aspx) carriers all kinds of replacement parts for Model T’s, including tires. You can also search for them on eBay Motors (http://motors.shop.ebay.com).