While we rely on imported farmed pupae from the Tropics, we have always had an active breeding program to boost the numbers.
Some of the specialist host plants takes years to source and then another two or three years before we have them big enough to try and breed something on them. If successful, that first test might breed five or six caterpillars on a plant before we run out of leaves, the adult butterflies of which then last just a few weeks and about ten percent fly at any one time. This is why butterfly houses are expensive.
It then can take another two or three years to multiply the host plants up so we can produce enough to make an impact in the display each month.
Even with enough food plants, our breeding programs are constantly hampered by ants, spiders, fungi and viruses all attacking and destroying many of our caterpillars. Breeding butterflies is a Sisyphean task!