Just do it. Here, I'll even give you what to post in an interest check;

"Hi, my name is Blue Tempest and I'm really excited about *franchise* and would love to RP in the universe. However I'm not very confident in my GM'ing abilities or my grasp of the franchise's lore. So, I'm looking for someone who likes the series and is willing to take up the mantle of GM. If anyone is interested in GM'ing, or even just joining a game in the *franchise* universe, please let me know by posting here!"