I assume this bass pond is mud bottom and fairly large. Here's how it's done.

Being able to lower the pond level and a clean bottom are a big help.

Other than that the methods you're using would be plan B. Not very effective as you've found. You might be able to get some but getting all would be tough.

Longer term you might be able to train them to come to food, they may have to re-learn this. Then you'd have more luck.

For bait I would use Berkley Powerbait for Trout, maybe Catfish. I know the Trout version smells just like the fish food they feed at the hatchery which is similar to many Koi food.

Not sure if you want them caught alive, but you can string a trotline. Or bunch of jugs (plastic soda bottles) with fish line and hook tied on. Fish would probably not survive. I'm pretty sure these techniques are legal in private ponds but you may want to check.

On a side note, the state of Maine out laws keeping of Koi and Goldfish. Many people think that's unfair, and maybe it is. But this demonstrates why most people in the state don't want to take the chance.

All I can think of would be to get the water as low as possible and get the waders on with 2 or more people with nets and herd them into the nets... Koi even in a foot of water and small ponds are tough to catch the can dodge, jump and flip right out of a net.

Don't try to hook them! Koi have very soft mouths that will tear and infect very easily. They also tend to die from stress. Lowering the water, if possible, is the best option. A weighted drag net, to push them to one end, then hand net, is the best solution. An old soccer net can be used to make one cheaply. I've also used the orange plastic fencing you get in a roll from Lowes. I don't know how deep your pond is. Otherwise, enjoy your new fish!

I reread this thread and I am still not sure what the problem is. The koi look nice and the little ones will make good bass food.

You're lucky the pond isn't in Florida, the Game and fish folks here take a dim view of escapes of exotics. Depending on species they have been known to kill everything in a lake to prevent spread.

fish for them. don't worry about hooking them.....they will quickly become a huge problem in that pond. If they start breeding in that pond, you will never get rid of them unless you drain it and start over.