I would check PerformanceNashbarSupergo or whatever they are these days. Also look at Pricepoint and JensonUSA. And here's a little secret for you, if you know the specific product you're looking for: qbike.com.
For riding my BMX in the snow, I just wear my race pants, which are about 200 billion degrees.
I purchased some thermal tightes from the 'hunting' section at WalMart and sew'd 'stirrups' onto the bottoms of the legs to make sure they stayed down over my ankles. They were like $10 and although they aren't quite as nice as cycling-specific tights, I can have a different pair of these to wear everyday for a week for what one pair of cycling-specific tights would cost.
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