Can't vouch for this company nor do I know their prices, but they ship prominent names in cloth, such as H Lesser, J & J Minnis, John G Hardy, Scabal,
Holland & Sherry, Smith Woollens, and Hunt & Winterbotham anywhere in the world
http://www.finetextiles.co.uk/
There is a company a few doors along from them at 99 Regent St. called the London Textile Co who run a similar business. I have never used them so I can't vouch for their service or prices. They don't have a website but their phone number is +44(0)20-7734-0833 and email address is: thelondontextiles@hotmail.com.