you can buy them off eBay
There are a few card reader you can buy but they are hard to get nowadays so I would say buy an arduino and do this: http://hackaday.com/2011/03/20/gameboy-rom-backups-using-an-arduino/
It's called an Action replay, it's a black cartridge with a holder for your game, and has a red circle on it with "action replay" in the red circle written with white. You can buy them for different size game cartridges (one for Game boy games, one for DS games) and you can find them at Walmart.
No most Game boy games are non violent but it depends on what game you buy.
walmart
You can check out the Dell site for new ink cartridges for your printer. Also check Amazon.com and Ebay.com for great low prices everyday of the week.
You can buy them at the market near my house
You must be at least 16 years old to buy C02 cartridges.
You can buy larger expansion battery packs for the Game Boy Advance that last much longer.
Ebay or VideoGameBoxProtectors.com
Research has shown that one of the best and cheapest site to order ink cartridges from is 4inkjets.com. This company has been awarded a circle of excellance platinum award for their services.
A great place to buy replacement ink cartridges is Amazon.com. They offer a wide variety of ink cartridges for nearly every printer on the market. It is okay to use refurbished ink cartridges, however it is preferred to buy new ones.
Depends who you buy it from