It seems that boosts are not dropping now that teamups are inplace. It is posible that in the code Teamups took over boosts for drops.
If this is the case are there plans to make boosts drop more frequantly in other methods?
Progression rewards come to mind, you could further split up the progression ladder into sections of 25 points (the base amount to earn when entering an event) and give out the boosts that way.
As it stands now. there is not a way to replenish them.