Because Spring is a tricky time of year for fish, I lower my pond water and catch the babies in Sept.......leaving Spring as a time to restart things gradually.
If you have your heart set on another jumbo tosai, If I were you, I'd lower the pond water and catch many goldfish to rehome before cold weather comes. I plan in advance where mine are going.....some years I've been lucky to give them to friends with ponds and other years I release them in a natural pond on the grounds of one of our favorite plant nurseries......with their permission of course. This is a large pond, filled with lotus, lilies, turtle, frogs and a variety of fish.....I know they may become a meal for a predator, but at least they have a chance.
Lots of serious koi keepers get new fish, but they are constantly rehoming their stock.....I personally am too emotionally attached to mine. I don't know how big mine are....somewhere between 2-3 feet. Three of mine are just "pond mutts" from the fish hatchery and one is from a breeder.
I've seen that food on Amazon for less too, however Tom told me theirs is specially formulated......whatever, I'm sure they're basically the same thing. Ayway, I've been buying from him for years now....BTW I buy the medium sized pellets. I've used large pellets also, but they seem to prefer the medium sized ones.
PSKoi is located outside of Indianapolis, having relocated from California due to the high cost of doing business there. I believe he flies his koi into O'Hara .
Another option would be to re-home some fish now and dream all winter of a new tosai for next year