Hello, and welcome to Serebii! As EVs/IVs are something I have a decent degree of understanding of I'll post a brief explanation here. If you're interested in more you can find great guides and information here on Serebii, as well as on Smogon and Bulbapedia for these sorts of mechanics.
Also, as I understand, some people are willing to trade Gamestop codes and similar such things for other events and rare Pokemon in the trade forum, although such is obviously a trust trade and I'd recommend only trading such items with well-known and respected traders.
EVs and IVs are values assigned to each individual Pokemon that help determine their stats. Each Pokemon has a certain number of IVs in each stat, from 0 to 31. These serve as "bonus points" for that stat, adding 1 point to the visible stat for each IV by level 100. So a Pokemon with 31 IVs in a stat would have 31 more points in that stat than the same Pokemon with 0 IVs in that stat would by level 100. A Pokemon's IVs are randomly generated when it is caught (except in the case of breeding, where 3-5 IVs may be passed on from the parents), and currently cannot be changed, but a process called IV breeding will allow you to breed Pokemon with flawless or near flawless IVs. It's a tad bit too complicated for to to put in a short welcome post though.
EVs also add to a Pokemon's stats, but in a different fashion than IVs. Where 1 IV = a 1 point increase in the visible stat, 4 EVs = a 1 point increase in the visible stat. Pokemon earn EVs by defeating wild Pokemon and through the use of vitamins, unlike IVs which are randomly generated fixed numbers. Each Pokemon can have 510 EVs total, and 255 in any one stat (although 252 is the largest number divisible by 4). Power items (Weight, Anklet, etc) all add 4 EVs to their respective stat on top of whatever EVs a Pokemon gives naturally when defeated, so for instance defeating a Scolipede while holding a Power Anklet will give +7 Speed EVs to that Pokemon. Vitamins like Calcium and HP Up add 10 EVs to their respective stats, but cannot be used if the Pokemon has more than 100 EVs in that stat. Certain berries (Pomeg, Qualot, etc) take away 10 EVs from a stat and increase happiness, which is useful if you accidentally get EVs in a stat you don't want to train. If you want to see which Pokemon give which EVs, Serebii's Pokedex has that information, as well as a function that allows you to search Pokemon by EV gain.