I always have to go with the old Popeye cartoon "Never Kick A Woman" in which Olive Oyl is at first beaten, then beats up a sexy blonde. I'm still not sure if that caused my interest in f/f fights or if it just triggered something that was already there.
I do remember Foxfax - it had photo-shopped pics of celebrities who were in a femme fighting league, drawings and links. I loved it but it didn't last long. That was early internet days, around 1998 or so, I think.
I used to send in stories to Cavalier and Nugget with both celebrities and just thinly-disguised versions of women I knew matched up in fights.
All I can say now is thank goodness for the internet. It has made following our little fetish so much more easy, cheaper and fun.