Same here, I don't know anyone who might send me an invite unfortunately. It's unlikely for this topic to come up organically in a conversation as in "hey by the way are you on lobste.rs" so my previous attempts were by sending messages in my company's notice board asking if someone is there. But in the last few years I have worked in smaller startups so the sample size is too small for this strategy to succeed.
FWIW, folks on lobste.rs are (mostly) friendly and willing to extend invites if you seem like a real person. My understanding is that the invite system is primarily in use to avoid drive-by spammers and the like.
Feel free to send me an email (findable via my HN profile) mentioning that you found it via this thread, and I’m happy to extend an invite.