If you use the good sam search engine for finding campground the season they are open is always listed I have found them to be 100% accurate
Under Park Features select "open all year"
Example
Lat, Lon: 36.37, -105.59292
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Facility
7.5 Restrooms
8.5 Appeal
8.5
Card(s) Accepted: Debit, Discover, Visa, Master Card, American Express
Last Year's Rate: $35 to $46
Season Open All Year
Elevation(ft): 7,151