There wasn’t really a definitive answer, but this might be a good place to start: www.elitefourum.com/t/how-did-card-distributions-for-battle-road-tournaments-work/24911/1.
Assuming both from the PCG-P set, the Mew and Charizard you mention are both participation prizes. To my knowledge this means that everyone who participated in the relevant Battle Road tournaments (usually spread across 8 or 9 different locations) would be awarded one of those cards - one of the posts I made speculated that one of these tournaments may have had 864 participants per venue, meaning we can assume a distribution of around 7,300 of each participation card.
That said, distribution isn’t everything. The much rarer finals prizes tend to fetch significantly less than participation prizes if they do not include popular Pokémon (like Mew or Charizard, in your case). As a great example of that, last year a PSA 10 Rainbow Energy from the PCG-P set sold for around $50 on eBay at auction; in theory there are 10-12 Mew cards for every one of those printed.