[B.Scott]

In order for your filter to cycle the bacteria need to grow ooty. Unfortunately, as Mike suggests, this isn't going to begin before the water temperature gets into the 70°F range

What follows amounts to closing the barn door after the horses have escaped but...

The time to add ANY fish to your pond would be in about 6 months. You would have been better off waiting until that time to purchase fish. You are by no means alone in this mistake. It's an age old story of people spending all summer (or slightly longer) building their dream pond and then filling it with fish in early to late fall. The trouble starts with the water temperatures starting to fall and the bacterial development in the filter screeching to a halt. There then follow ammonia and nitrate problems and the fish develop health problems. Then at some point chemicals are added to the pond which in most cases hammer the already fragile filter bacterium even harder leaving the system in a state worse than in the beginning. It is a vicious cycle and an introduction to the hobby that causes many prospective koi keepers to leave the hobby prematurely.

Ooty I fear you are in for a rough ride and there is very little you will be able to do to prevent it.
Your first option is to learn from your mistakes, take the damage that follows on the nose and replace the fish you lose later in the summer when the filtration is finally up to scratch.

If the first option seems unacceptable you could try either heating the pond to 70°F all winter (NOT CHEAP!) or removing the fish to an (indoor?) cycled quarantine tank and postpone the pond start-up until June.

I don't envy your choices and wish you had gotten access to a little better info before you took the plunge, if nothing else, from the guy who sold you the fish. Did you get them from a dealer?

Good luck

B.Scott