Pictured below, the mega stone charms in question and their original components (for ease of scrolling…and likely not to relative scale :P).
Thank you all for your assistance. <3
On the good news, recently nabbed a Reshiram dot charm and Shiny Mega Rayquaza charm from the interwebs; next in line, the multi-week shipping wait. Whee!
EDIT: Sold-out/price-rising nerves got the better of me and I had since bit the bullet and purchased a full set of Mega Latios and Mega Latias charms. More good news, I forgot I already purchased the Mega Charizard X set! XD Only leaves the Reb Orb then, which might be more of a long-term mulling over slash as opportunity presents itself. :)