If you don't see a proper category or subcategory to submit your article to, ASK FOR IT!
Every article directory out there will usually not have a problem adding a category for your article(s). Just do a quick search to see how they want you to do it.
If you cannot find how to do it, you can either email the support address, or you can try what I have my authors do...
In the first sentence of the article body, SUGGEST THE NEW CATEGORY IN A SENTENCE WITH ALL CAPITAL LETTERS.
Nothing is worse for an article editor than getting an article submitted about, say, Plastic Manufacturing and having it submitted to the "business" category!
It only takes a moment to create a new category, and it will help your article with SEO by getting more appropriate words on the page!