From Wikitravel

                                 Melchor de Mencos

Melchor de Mencos is in Guatemala on the border with Belize and is usually a place that most travelers merely pass through, but it does have some stelae and zoomorphs in a square not far away. From the border, go to the first main road to the right. It is off to the right maybe a 20 minute walk away.

Tikal Travel there can arrange a number of tours, including Yaxhá to Nakum to Tikal. It is located at the Río Mopan Lodge