You should add some benefits for joining a clan like donating blueprints or something.

Like put a chance:

A)To request 10 uncommon blueprints once a day.

1 rare once a day.

1 epic once a week.

1 legendary blueprint once a month.

Also get some  blueprints fragments which can be used in all mechs or weapon.

Eg:if you have 500 blueprint fragments it can be used as 500 uncommon blueprints or 100  rare bleprints or 10 epic blueprints or 1 legendary blueprints.