Keeping koi carp requires some specialist knowlege. We are not experts and cannot give advice about specialist koi pools. The filtration equipment that we offer is intended for general fish ponds, but can be used for some koi providing that the filter has enough capacity.
Koi grow larger and faster than other fish. They eat more food and produce more waste. For this reason it is recommended that a filtration system with double the usual capacity is used if you wish to keep koi. Put another way the fitration capability of a filter published on this site is for "other fish" and should be halved for koi.
If you want to learn more about keeping koi we offer some books for sale on the subject. There are also some informative websites:
http://www.vcnet.com/koi_net/ponds.html

Azpack Limited, 12 Kernan Drive, Swingbridge Trading Estate, Loughborough, Leics,
LE11 5JF, England. (01509) 261256