They Bred Moya. But no Leviathan gunship survived the birthing process until Talyn. And it was Chricton and the crew who figured it out. That was why Talyn was crucial to the Peacekeepers. They had hope he'd be the first of a new generation of warships.
And they purged the one guy who knew how to do it and apparently had 0 backup or oversight of the research...
Talyn was suspected to grow to twice the size of Moya and he would have started growing more weapons and defensive systems. He may have even grown his own defense screens. A feat that would have been monumental. Say what you want about the Peacekeepers (and I say a lot with none of it being good) but when it came to designing Organic warships like Talyn they really outdid themselves. Talyn was a thing of beauty.
Well, given that they couldn't bioengineer themselves to survive the Heat Death I am not that impressed.
Also, I think that there were quite a few Leviathans around, since the convoy Crais was overseeing had lots of them IIRC.
But if they want to bolt guns on them they can probably use the Bulgerian approach to training gusrd dogs.
The dog gets put in place while a puppy, then some stranger comes into the yard and lures it in with food, only the food will make it ill later and then beats it so that it must learn that strangers must be attacked and never trusted.Only the household members are 'good'.
That and cutting off their ears and feeding it to them to make them more vicious.
So, Leviathans can be "captured" by "evil pirates" who will do lots of damage, torture the Lecisthan, maaaybe kill it's pilot, then the PKs come in and "save the day".
Oh, yes, we will take care of you, poor pacifist space whale, but could you perhaps help us in our quest to rid the galaxy of these degenerates.
We will even repair all the damage either out tech and, err, improve things.
So you get a vengeful space whale janissary with extra weapons bolted on that thinks it owes you it's life....