HEC-GeoHMS is legacy software. The official final version compatible with ArcGIS 10.8 is HEC-GeoHMS 10.2.2 . There is no “exclusive” newer version beyond this for ArcGIS desktop, as the US Army Corps of Engineers (USACE) has shifted focus to HEC-HMS integration with QGIS.
provides legacy versions such as 10.2 and 10.1, though these may require compatibility adjustments for 10.8. Arc Hydro Tools download hec geohms for arcgis 108 exclusive