https://www.cosmosfarm.com/threads/document/20533 를 참고했고 2뎁스까지는 진행하였습니다.

추가로 form에서

<input type="hidden" name="kboard_search_option[tree_category_3][key]" value="tree_category_3">

<input type="hidden" name="kboard_search_option[tree_category_3][value]" value="<?php echo $board->tree_category->getCategoryNameWithDepth(3)?>">

html에서

						<?php if($sub_tree_category_list):?>
							<ul class="sub-tree-category">
							<?php foreach($sub_tree_category_list as $sub_item):?>
								<li<?php if($board->tree_category->getCategoryNameWithDepth(2) == $sub_item['category_name']):?> class="kboard-category-selected"<?php endif?>><a href="#"  onclick="return kboard_tree_category_search_2dapth('<?php echo $item['category_name']?>', '<?php echo $sub_item['category_name']?>')"><?php echo $sub_item['category_name']?></a>

								<!--추가-->
								<?php if($sub_tree_category_list):?>
									<ul class="sub-tree-category">
									<?php foreach($sub_tree_category_list as $sub_item):?>
										<li<?php if($board->tree_category->getCategoryNameWithDepth(2) == $sub_item['category_name']):?> class="kboard-category-selected"<?php endif?>><a href="#"  onclick="return kboard_tree_category_search_2dapth('<?php echo $item['category_name']?>', '<?php echo $sub_item['category_name']?>')"><?php echo $sub_item['category_name']?></a>								
										</li>
									<?php endforeach?>
									</ul>
								<?php endif?>
								<!--추가끝-->

								</li>
							<?php endforeach?>
							</ul>
						<?php endif?>

스크립트는

function kboard_tree_category_search_3dapth(category1, category2, category3){
	jQuery('input[name="kboard_search_option[tree_category_2][value]"]').val(category2);
	return kboard_tree_category_search('3', category3);
}

이렇게 추가하였습니다.

2차 카테고리에 맞는 3차 카테고리 자체가 안불러와지는데 어떤 방법이 있을까요?

감사합니다.