Fetch partitions where values are present
SELECT DISTINCT
       format(
          'calendars_y%s_m%s',
          lpad(CAST(extract (year FROM q) AS text), 4, '0'),
          lpad(CAST(extract (month FROM q) AS text), 2, '0'))
FROM (VALUES (DATE '2021-01-01'),
             (DATE '2021-02-01'),
             (DATE '2021-02-02')) AS q(q);

       format        
---------------------
 calendars_y2021_m01
 calendars_y2021_m02
(2 rows)

But I seriously doubt that it is a good idea to do that on foot. You will be better off letting the PostgreSQL optimizer figure out which partitions to scan.