The only decals you can find every once in a while are the newer 2006/7 decals. Those '78-'79 decals haven't been available for decades. You may be able to find some reproduction '83 decals on eBay (there was a seller with some for a while), but they are a slightly different color scheme than yours. They are roughly the same shape, but they might be a little larger too.
The only other choice is to have a graphic shop try to replicate your current ones, of course enhancing them to original colors. If he needs a color sample of what they looked like, you can pull off your entry door (make sure to replace the putty tape when reinstalling). The striping will go under the door slightly and you can get a little slice of original colors there.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9473.8 (as of 6/18/21)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR