Hi, you can get the lens by beating the tentacle monster during Mei's story.
If you've already sold the security card and can't access the monster, this is an oversight on my part, I'm sorry. It will be fixed in the next update. If this is the case though, you can get the card back by opening the console (Shift+ O) and type in "mc_inv.take(cavelabcard02)", without the "".