The plugin is available in QGIS Official Plugin Repository, that repository is recommended. An alternative repository is here (to be used in QGIS plugin manager): http://blazek.github.io/lrs/release/plugins.xml
Direct download (1.2.3) for QGIS 3
Direct download (0.3.7) for QGIS 2
Developped by MPA Solutions in collaboration with Provincia Autonoma di Trento - Dipartimento infrastrutture e mobilità - Servizio Gestione Strade - Ufficio Controllo e Tecnologie Stradali.