So is it like the kits are only temporarily available or something? And where do I buy them? Thanks for replying by the way ?

I recently returned to the game, and was searching the Garage for the next Product Kit to go for. However, I can't see any place for kits in the Garage. I can see Product Kits in the Shop but they can only be purchased with Tankoins. You can even see here that Bulldog Mk4, which is supposed to be buyable with crystals at my rank (according to the wiki), is only buyable with Tankoins. So I have a few questions. Is it still possible to buy Product Kits with crystals. If so, how? I noticed I could only see Mk4 kits in the Shop, even when I was at a rank to get Mk3 kits with crystals (according to the wiki). Why is this? Some information about my account: It's an old account from before the "Mk" update. I have one Mk3 turret, one Mk3 hull, and 3 Mk3 protections.