There are a few publications about Vampirella which weren't produced by Warren or Harris. Some are one off's by other companies, some are "fanzines".
The magazines created by fans (a.k.a. the "Fan-Zine") can often be a lot more elucidating as it is not dictated by the same editorial policy/politics as the official publications.
There are a few odd publications out there, each of which has a varying level of rarity.
So far I have found/listed the following ...
If you know of any more that should be listed here please contact me.