What I do is usually make a code out of it if I have an action replay. But right now I'm assuming that you don't have an action replay.
An alternative would be to download a program called "shinyGTS". You can find it by searching google and clicking on a link to this website. Then when you open it, you need to know your local IP address which can be found by opening the command prompt and typing "ipconfig" and pressing Enter. Then where it lists IPv4, that is what you must type into the IP field in shinyGTS. Then start that server. Then on the right side of the program, click on the appropriate selections, then add the pokemon or folder of pokemon. Then click start server for that side. Now go into your wifi options on your NDS. Go to your set up and switch "Auto obtain DNS" to off. Then edit it to the IPv4 address that we found earlier. Now go to a wifi trade in your game, and once you get into the wifi trading room, you will have all your pokemon collected. Make sure that you put them all in a box so that their stats become what they're supposed to!