is there a way to get a mdl in untiy

mdl is what valve used to create models for half life 1 i want to take models from half life 1 and put them in unity how do i do that

Unity can read .FBX, .dae (Collada), .3DS, .dxf and .obj files

You will need to find some sort of exporter/importer plugin between mdl and these formats for your 3D modelling app to get them into a format that Unity understands.