The path to the key card starts at the chemical plant with professor dvupalov, after you grab the crystal thorn artifact for him. Once that's done make your way to ahroprom factory north of rostok, where youll find shcherba hiding behind white curtains near four water tanks outside a rusty building. Just talk to him about dvupalov, and he'll hand over the x5 key card along with an optional task about some documents. The lab entrance itself is underneath ahroprom, through a sewer hatch by some storage containers. Maybe interesting - theres a decent ssp-99 suit behind those curtains near shcherba that'll help with radiation and psi protection which youll definitely want since the lab's got controllers making phantoms down there. Good to know, the outside of ahroprom is pretty dangerous with patrols and anomalies everywhere, so grab what you need and dont hang around too long. Psi-block items are absolutely worth having before you head down into the lab, trust me on this one.