Prostar 90 Plumbing Help

[Sasarsis]

I have been searching for a while now and I am having a ton of trouble locating plumbing parts for the Prostar 90 return. Specifically I am looking for the threaded adapter that attaches to the bulkhead. Is there a good place for this part online? I bought this tank recently from someone who bought it new and didn't end up setting it up. The return section was missing and I am trying to piece it together. I know it is metric which has been the biggest hurdle for me finding the parts since I am in the US. I can run it as it was originally intended or I can switch it to tubing. I just want my sump working. My LFS sells Red Sea but couldn't help and Red Sea's customer service is TRASH in my experience. I haven't received a response to either of my two inquiries. Any help would be incredibly helpful. Thanks!