Method 1: Purchase a copy of Maniac Mansion on eBay or such. Download a single copy of the data files. Load and play them in ScummVM.
Method 2: So, funny story. See how Day of the Tentacle Remastered is for sale above? It just so happens that the original Day of the Tentacle contained a computer that allowed one to play Maniac Mansion. The Remastered edition above ALSO contains that same computer with that same copy of Maniac Mansion. So if you buy Day of the Tentacle Remastered, then play up to the point where you reach that computer, you can play the original Maniac Mansion.
Yes --- there's a copy built in to Day of the Tentacle.
Go to Weird Ed Edison's room and use his computer, and it'll start up. Or, well, it used to. I've only ever played it on ScummVM, which didn't support that opcode, but it was trivial to haul out the data files and run them separately.
I have no idea whether the remastered version still contains this. I hope so (I've never finished Maniac Mansion).
