Maxxis Marauder and Mickey Thompson SR (NOT the ST) are both H speed rated (130 vs the V at 149) and reasonably priced and available in a variety of 15" sizes through a variety of outlets.

Z rated tires are available in the Avon CR6, but they are not cheap and their d.o.t. approval is marginal. These are race tires parading as a street tire for vintage race cars.