There's no way that I found to get endless lava and I couldn't find lava in the prison op server shop... So is there a way?

 

OpPrison? Vote parties.

 

You can get lava buckets from vote parties. They're also auctioned frequently after a vote party so if you don't get one during the event, be sure to keep your eye on the auctions.

 

I'm pretty sure she means Normal Prison.

 

Locking as inactive.
If this is still an issue feel free to open another thread.