I would suggest you post a topic like that in the General Discussion thread, as that has been done before.
Now, one scenario has just started signing people up, and that might be something your character would like to participate in, or it might not. Usually, at least once a month, you get a scenario started.
Otherwise, if you have a specific idea for a White Scenario that you want made, but don't want to GM it yourself, these are common as well. Post in the General Discussion thread with something like, looking for GM, GM wanted, whatever.
Or, if you just want to participate, just wait around for anther scenario to be created.
If you really want to get into it, Game of Patience is signing people up right now, and there should still be room for a few more people. If you have a Yuku account right now, go ahead and sign up for it if it's your thing. Otherwise, you will either have to GM one yourself, or wait a few weeks, maybe less, to get in one.
You can really never tell when a scenario will be put up. If you want to know the frequency of starting scenarios or so, just take a look at the 'scenario request' thread on the boards. That shows you when they were each created. You might have a month between scenarios, or you might have, in the case of myself and Rhan Komo's scenario, only a few days. It just depends on when a GM gets a story down and has time to do it and all.
Hope this was helpful! If you have any other questions, feel free to DM me or post them here again!
Disclaimer: This post may or may not contain stupid material.