I have a question about Buddy Complex production.
No tag exists for this series yet, but I also do not have the tag creation privilege here.
What tag should I use?
senshin already answered this in the comments, but I'll add an answer just for completeness.
Currently, our suggested work-around for this situation is to use retag and clearly state the name of the series in your question (and, if it isn't obvious, the intended tag name). A user with sufficiently high reputation will edit the proper tag in. This usually happens almost immediately, but if it doesn't within a day or two you can flag for moderator attention requesting the tag to be edited.