do you mean the Hehr vents that are 12X12'ish square, with the lifters? Inland, and also most RV supply shops have plastic covers that can replace the old aluminum cake pans that were up there, though you might have to do some adaptation to the cover to get the lifters to attach. There's a website somewhere that details it. You can also replace the whole thing with a Fantastic Fan Vent. It's what we're considering for our Safari.
If it's plumbing vent covers then both Inland and Airstreamdreams.com carry them. If you're talking stove or fridge vent, I haven't looked into them so check the above mentioned sites.
PS, is your Safari working, do you take it camping? If so, maybe we can meet up at a forum rally and exchange notes!