Evolving Weapons and the shop

I recently got a blue sniper canon and was able to get it to evolution level, but didn't evolve it yet. Apparently I need to get another blue sniper canon to make the new evolved one, so I head on to the shop to buy one, which is really expensive, but in the shop where the buy button is, it just displays a green ticker indicating that I got it! So my question is, why can't I as a player buy as much blue cannons as I want! Since it's extremely a rare chance to get a blue weapon, and more extremely rarer to get this item exactly, why can't I buy one with my hard earned f2p money!! It doesn't make any sense!!

 

im guessing they want you to buy pearls and get the blue cannon through opening epic boxes also sold at the shop. not doing so would be a frustrating wait of months opening the free cheap boxes that hardly gives out rare items.

 

This'll explain how the system works.

 

Also...it's free to play...so enjoy that aspect. if you never want to pay for something you get for free, then grind away. it's possible to get another rare cannon...trust me...you'll open enough boxes that you'll get one soon. just stick with it bro!!