I don't think they are making them anymore, but I'm sure GameStop will have some or Amazon.com
Buy a new one.
Simple buy the game new in the collector package
Amazon has new copies but they are $47. Used games start at $5.80
At this time it's hard to find new copies of old Pokémon games anymore. You can try looking for them on eBay, but be sure you buy original copies and not bootlegs.
Buy new Pokemon Ruby and play it.
You cannot buy but you can teach your pokemon new moves in exchange of shards.
buy a new one or start a new game
You could only buy them in Eba but there is a new version of Pokemon gold its Pokemon Heart gold but its very expensive its $39.99
its a Pokemon rpg were u can battle Pokemon, earn platinum coins, battle other trainers find rocks, DNA ,wild Pokemon (you can catch them with pokeballs) buy stuff from the shop or buy new Pokemon the URL is tpmrpg.net
when the game comes out, people buy it at a high price and millions of copies are sold. Later on when another new game comes out. The first game sells less copies, therefore becomes lower on value so more people buy it.
the only real thing you can do is start a new game or buy a new one
No, because they are copies of the original Pokemon, so if you don't start a new game, the creators figured you didnt need a second set of all the Pokemon you already have