I was looking around on Google Earth again for more possible mud locations, and I found the best one. It's even better than the abandoned boat ramp I found back in September.

Of course it's all frozen (Most of our snow melted, still have ice), but there was still some unfrozen water a few inches under the surface.

It's a 2000-ish foot long narrow lake that starts a few hundred feet out from the road, but curves inward so only a little bit of it is visible from the road. The last 100-ish feet of it is a few inches of ice in the center with the rest being cracked frozen mud, the crackes being 1-4 inches wide. At the very end is a depression spot that was all frozen ice, but didn't look more than 2 feet deep.

Hard part is having to wait 5-6 months for winter to end and snow melt to evaporate before I can really tell how good the mud will be.
I'm keeping the location a secret in the meantime, but I'll definitely make an update post this summer.