I am looking for a complete wiring harness for a 1964 Olds Dynamic 88 convertible. Wanting to go back to original. Has an after market in it currently.

 

Try to find out what other years, and makes are the same. That might broaden your chances of finding one. I got two junk ones off ebay (20eh) and made one good one out of them. Mine was brunt/melted in a couple places.
Find a Seller with parts to your car and email them an ask them if they have what you need.
Fuse-box? Motor harness?, etc...
This is just an idea to help you out.