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You can get one copy of each per BW2 Save File and per Dream Radar Save File - so if you wish to receive them more than once, you'd have to restart BW2 AND restart Dream Radar/restore a Dream Radar save backup with the genie unsent (if you can access the SD card in your 3ds, backing up the SDMC:\Nintendo 3DS\*\*\00040000\000ae100\ folder will copy the save data and the game app files without you needing to restore your entire SD card - just backup/restore this folder as required. Oh, and * = 16 random hex values, they aren't overly important).
You can receive them in-game as soon as you have the PokeDex - if you do it before the first Gym then they'll come at Lv 5.

Thank you very much! Now I need to think about if I should restart my game or not xD Or perhaps buy an already used White 2

Heh, no problem! If you have access to 3DS Homebrew (if you don't then I would recommend it - SoundHax is free, works on the latest 3ds firmware and takes only a few minutes to set up), then you can use a neat tool called TWLSaveTool to backup and restore your retail cart saves for NDS games, which would mean that you only need one cart (you can just backup your main save, restart the game, RNG Therians to your heart's content, and then restore your main save).
If you don't have access to Homebrew then yeah, I guess you've either gotta restart or buy another cart :/