Google says GearTrade has a few pairs for reasonable prices New & Used Bike Socks | Socks | Buy and Sell Men's Outdoor Clothing
Maybe for the short term / test my theory:
- put some thing thin mesh under your insole - maybe get some of those mesh bottle protectors from the liquor store or a few layers of screen door material. Maybe put a layer over the cleat, then a vapor barrier (packing tape), then another layer of mesh, so you get two air pockets over the cleat heat sink.
- Put a sock over your shoe, under the cover. Maybe raid the lone-sock bin for some wool/nylon/acrylic socks and only cover the forward section. Maybe put a bottle protector over your toes too.
really glad they don’t actually sell “Used Bike Socks” here. 
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If it’s in your budget ($300+), I suggest trying a good winter boot. Most aren’t much warmer than shoes, but my Lake 303 boots make a huge difference. Lake has replaced that model with the 304, which looks similar. The insoles are fantastic, and the boa and body are very sturdy, but they aren’t brutally heavy.
My feet are sensitive to cold, and I use the Lakes below 40F/5C. Below freezing, I put overshoes over the Lakes, and below 20F (-7C), I put chemical hand/toe warmers between the overshoes and the toe box of the boot. Below that temp, I am out for only an hour or two anyway because my water bottle freezes. I use only one sock, and it’s not very thick (circulation is key). It’s an expensive solution, but make outdoor cycling a viable option for several additional months each year.
Because they are a bit larger than cycling shoes, they cause a bit of toe overlap and require larger sized booties.