It's great if you have to time to wait -- and eventually find one, but in the meantime you could consider a temporary solution. Then when you find what you want, you can sell the "temporary" one. That's basically what I did. They don't lose value at all.
The IV might work as a temporary or as a permanent alternative -- I don't know, but I would imagine that much depends on the film format you are using. If you don't use the full IC of the lens, a smaller CND filter probably will work fine. Easy enough to test.
I had the opposite problem. I had to go to a larger CND filter.