I was under the impression that all Ilford and Kodak film was DX encoded. But if it isn't, your easiest option is to use exposure compensation. The N/F55 will default to ISO 100 if it doesn't detect a DX code, so underexpose by one stop to achieve ISO 200 and two stops to get ISO 400.
You may still be able to find DX code stickers, but the only ones I've seen on sale recently are for ISO 40 and ISO 125.
If you want to photograph a man spinning, give some thought to why he spins. Understanding for a photographer is as important as the equipment he uses. - Margaret Bourke-White