[yokohama]

I can only speak from personal experience but early in the year seems to be a good time to buy. Dealers getting rid of old stock, the number plate change coming up in March and making space for the new season's models. I'm not sure whether there would be much discount on Triumphs though. They tend to sell themselves.
Ebay is a good place to look. Search for a bike, filter for 'new' and work down from the high prices. Pre-registered models on older plates or with delivery mileage can be found at discounted prices.