while it might be beneficial to have such a section for those that use it, we believe that the market is rather small for such RPs. Right now, the sections are divided up into seven sections. three sections for post lengths (free, casual, advanced) and four for specific RP types. The specific types are Arena (which is competitive RPing specifically based around characters fighting each other), Tabletop (which is for those who want to play tabletop RPs that are heavily into dice and complex systems), Nation (which is where players control a nation/faction/or similar rather than single characters), and 1x1, which is where two people write a story on their own.
The type of RP you describe could fit in under several of these categories, so it does not make sense for it to have its own. 

However, if the proposed system for adding tags to RP threads is implemented, we can easily see the option for there to be a tag for RPing with canon characters.

New subforums is not something that is made without there being a huge demand for it. The Tabletop and Nation RPers had to wait a long time before they got their sections.

In the meantime, we recommend that you mark the titles of your RPs with something to indicate that you want Canon characters to be used. Do not find yourself discouraged if most don't want to play with such. If its sufficiently marked, the ones that don't want such will simply skip your thread(s). We can't say anything on how many there are with your same interest, but there's bound to be others out there.