The Toys R Us event didn't have any old sea charts. Mew was traded directly to your gameboy. The old sea chart was from a Nintendo event. I'm not sure if it's possible to mix records with a person who has it, in order to get it onto your game.
Yeah Nintendo events like the one at Toysrus recently is your only hope. I took advantage myself and got 3 mews (bold, docile, sassy) - one for each version I had. Now if only they'd have another event nearby and offer Lugia, Deoxys, or Celebi...