Hi Nicola, and welcome! You can certainly try to find a buyer here, just post what you would like to get for them and approximately where you are located (so shipping can be figured out).
You will probably get interest on these if you list them on eBay, too. It will help to state what condition they are in (are they written on?) It is good that you have some of the mailing sleeves still too.
I don't think any of these are very scarce, but I am not a calendar specialist so someone might correct me.
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