fender mounted turn signals

Punch "68 Dart GT fender mounted turn signals" into Google and all sorts of pages will come up with them for sale.
The '69 ones are much harder to find. Especially good/used. Beware that they are almost 50 years old and will almost certainly need new lenses and bulb assemblies. The housings corrode, and the lenses get brittle and crack when you try to remove them to replace the bulbs.