Minimum & Maximum Quantity for Variation

functions.php

<?php 
add_action( 'woocommerce_product_after_variable_attributes', 'wc_variation_settings_fields', 10, 3 );
add_action( 'woocommerce_save_product_variation', 'wc_save_variation_settings_fields', 10, 2 );
add_filter( "woocommerce_available_variation", "woocommerce_available_variation_callback", 10, 3 );

/**
* Adding Min and Max field in variations 
*
* @since 1.0
*/
function wc_variation_settings_fields( $loop, $variation_data, $variation ) {
  wp_nonce_field('wc_minmax', 'wc_variation_edit');

  woocommerce_wp_text_input( 
      array( 
          'id'                => 'wc_min_quantity_var[' . $variation->ID . ']', 
          'label'             => __( 'Minimum Quantity Var', 'min-max' ),
          'value'             => get_post_meta( $variation->ID, '_wc_min_qty_product', true ),
          'custom_attributes' => array('min' => '1'),
          'wrapper_class'     => 'wc_min_max_clear'
      )
  );

  woocommerce_wp_text_input( 
      array( 
          'id'                => 'wc_max_quantity_var[' . $variation->ID . ']', 
          'label'             => __( 'Maximum Quantity Var', 'min-max' ),
          'value'             => get_post_meta( $variation->ID, '_wc_max_qty_product', true ),
          'custom_attributes' => array('min' => '1')
      )
  );
}

/**
 * Saving Min and Max value for variations
 *
 * @since 1.0
 */
function wc_save_variation_settings_fields( $post_id ) {
    if ( empty($_REQUEST['wc_variation_edit']) || ! wp_verify_nonce( $_REQUEST['wc_variation_edit'], 'wc_minmax') ) {
        return;
    }
    if ( isset( $_POST['wc_min_quantity_var'][ $post_id ] ) ) {
        update_post_meta( $post_id, '_wc_min_qty_product', $_POST['wc_min_quantity_var'][ $post_id ] );
    }
    if ( isset( $_POST['wc_max_quantity_var'][ $post_id ] ) ) {
        update_post_meta( $post_id, '_wc_max_qty_product', $_POST['wc_max_quantity_var'][ $post_id ] );
    }
}

/**
 * Applying Min and Max value on front end.
 *
 * @since 1.0
 */
function woocommerce_available_variation_callback( $variation_array, $this_something, $variation ) {

  $parent_id    = $variation->get_parent_id();
  $variation_id = $variation->get_id();

  $pro_min = get_post_meta( $parent_id, "_wc_min_qty_product", true );
  $pro_max = get_post_meta( $parent_id, "_wc_max_qty_product", true );

  if ( $pro_min == "" ){ // if parent min is not set then check for variation min
    $min = wc_get_product_min_limit( $variation_id );
    if ( $min != "" ){
      $variation_array['min_qty'] = $min;
    }
  }else{
    $variation_array['min_qty'] = $pro_min;
  }

  if ( $pro_max == "" ){ // if parent max is not set then check for variation max
    $max = wc_get_product_max_limit( $variation_id );
    if ( $max != "" ){
      $variation_array['max_qty'] = $max;
    }	
  } else {
    $variation_array['max_qty'] = $pro_max;
  }

  return $variation_array;
}