those old goggles are Smith Cascade "Regulator". There are replacement lenses for them on ebay, however, I'd probably just buy a new set of regular cascades because you probably don't know what model regulator frame you have...or you could just buy a set of cheap Dragon Rogues (fits same face shape as cascade and excellent anti-fog).
...and, I agree, smith I/O are sketchy. Half the people that buy them end up with horrible fog between the lenses (I was one of them). I went through 3 different sensor lenses and they were all useless. Like you, I ended up having to ride out the rest of the season with my cheap old cascades because they never fogged no matter what the conditions.