Legendary Boosts

Is there a spot to buy them online or does it have to be simply when they are in rotation?

Warzone: Halo 5 Guardians: Warzone XP Boost REQ Pack | Xbox

Arena: Halo 5 Guardians: Arena XP Boost REQ Pack | Xbox

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> Warzone: Halo 5 Guardians: Warzone XP Boost REQ Pack | Xbox
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> Arena: Halo 5 Guardians: Arena XP Boost REQ Pack | Xbox

thanks my dude.