Load custom page templates from plugin for custom post type

function.php

<?php
function wpse255804_add_page_template ($templates) {
    $templates['custom-template-1'] = 'Custom Template 1';
    $templates['custom-template-2'] = 'Custom Template 2';
    $templates['custom-template-3'] = 'Custom Template 3';
    return $templates;
}
add_filter ('theme_tourfic_templates', 'wpse255804_add_page_template');

// Single Template
function tourfic_single_page_template( $single_template ) {
	global $post;
	$page_template = get_post_meta( $post->ID, '_wp_page_template', true );

	if ( 'tourfic' === $post->post_type && 'custom-template-1' == basename ($page_template) ) {
	    $theme_files = array('single-tourfic.php', 'templates/single-tourfic-1.php');
	    $exists_in_theme = locate_template($theme_files, false);
	    if ( $exists_in_theme != '' ) {
	      	return $exists_in_theme;
	    } else {
	      	return dirname( __FILE__ ) . '/templates/single-tourfic-1.php';
	    }
	} elseif ( 'tourfic' === $post->post_type && 'custom-template-2' == basename ($page_template) ) {
	    $theme_files = array('single-tourfic.php', 'templates/single-tourfic-2.php');
	    $exists_in_theme = locate_template($theme_files, false);
	    if ( $exists_in_theme != '' ) {
	      	return $exists_in_theme;
	    } else {
	      	return dirname( __FILE__ ) . '/templates/single-tourfic-2.php';
	    }
	} elseif ( 'tourfic' === $post->post_type && 'custom-template-3' == basename ($page_template) ) {
	    $theme_files = array('single-tourfic.php', 'templates/single-tourfic-3.php');
	    $exists_in_theme = locate_template($theme_files, false);
	    if ( $exists_in_theme != '' ) {
	      	return $exists_in_theme;
	    } else {
	      	return dirname( __FILE__ ) . '/templates/single-tourfic-3.php';
	    }
	} elseif ( 'tourfic' === $post->post_type  ) {
	    $theme_files = array('single-tourfic.php', 'templates/single-tourfic.php');
	    $exists_in_theme = locate_template($theme_files, false);
	    if ( $exists_in_theme != '' ) {
	      	return $exists_in_theme;
	    } else {
	      	return dirname( __FILE__ ) . '/templates/single-tourfic.php';
	    }
	}

	return $single_template;
}
add_filter( 'single_template', 'tourfic_single_page_template');