The official OXM magazine says:
Recruit Packs will help you flesh out your arsenal, but it's probably worth saving for the better Reinforcement Packs. Rare weapons make a big difference in battle, and you'll also have a better chance of unlocking new characters like the surprisingly cute Volus Adept. Unlike in the world of football stickers, duplicate items aren't a problem - get the same gun twice, and it will merely upgrade the original weapon. If you've already unlocked the character on a card, you'll get training instead, giving that class a whopping XP bonus and unlocking new appearance options.
How do you unlock this race, or how rare is it?