Not my ad but saw these hub caps and beauty rings on Kijiji in Ontario. Not sure but thought I've seen the blue outline dog dish hubcaps on '72 Sprint cars. I assume they must be a relatively tough to find item and $50 seems reasonable, so thought I'd pass along the web address for the ad to any Sprint owners.
http://ontario.kijiji.ca/c-cars-vehicles-auto-parts-tires-tires-rims-MUSTANG-HUB-CAPS-W0QQAdIdZ466828893
http://ontario.kijiji.ca/c-cars-vehicles-auto-parts-tires-tires-rims-MUSTANG-HUB-CAPS-W0QQAdIdZ466828893