Horseradish Seeds?

I'm looking for horseradish seeds for my brother-in-law. I told him I could find in some of the seed catalogues I get because he only orders from one catalogue. Unfortunately, I was only able to find a plant and it's hard to transport a plant from here to there, and he would say it too much to pay for 1 plant. So if you can help, it would be greatly appreciated.

Horseradish appears not to produce seeds. We have never seen it produce seeds, and we have never seen seeds available on the market. The only way to propagate plants is to divide an existing plant or to take root cuttings. Your brother-in-law will have to buy a plant.