The Pikachu AR only appears inside god packs, which have an estimated probability of roughly 1 in 100 boxes (1%)
Now, consider that Meloku never got a line in the entire novels and was barely mentioned
Go west from there to battle Scientist Ed, who has a level 35 Weezing, a level 35 Electrode, and a level 35 Electabuzz
However, every so often, the TCG introduces an expansion that makes them just a tad more obtainable
If you don't have a particular Pokmon set in mind and just want to tear open some boosters then tins, which have a selection of packs hailing from several recent releases, are a good way to go - if you can find them that is
With that said, the black-red deck features some of the creepiest, spookiest, and most villainous entities that the House has to offer, so if you really want to play the toughest setting, see if you can take down the House together