Toilet trouble?

Hello, i have been trying to stop a leak in my toilet and i relpaced every gasket and mechanism only to find out today that the problem was the tank. It has a hairline crack on the bottom that runs from bolt to bolt (about 6 3/4 in.) We have tried to find a replacement tank but it is an innocent blush 1974 Gerber toilet tank so NOONE carrries them. Is there a way to repare it that will ensure it doesnt leak or spread? If not, where can we find one? We are in West Virginia but would consider ordering one to be mailed in. Thank you so much!