If I were single and actively looking for a relationship (the latter of which I think is a mistake in the first place), I'd put activities in my online dating profile that matched up with what could only be a fellow prepper even while avoiding the word.
Adding activities or hobbies like canning, gardening, hiking, camping (primitive or otherwise), hunting, DIY home improvements, making tin foil hats (just putting that in there to get a giggle of course), etc to your profile on ANY dating site would be a good start.
Adding interests like solar or wind energy, off grid living, Tennessee whiskey (Tennessee ANYTHING, for that matter), home made mead, fresh eggs in the morning, cooking on a wood stove, and watching Southern thunderstorms rage outside my bedroom windows.... those might also be helpful.
There is no such place (that I know of) that is SPECIFICALLY for preppers. But if you catch a grasshopper by putting ^ THAT bait out there, I'd be very, very, very surprised.