Summary - Updated 9-21-12
Here are a couple of excellent sites that enable you to find Triumph OEM part numbers
Triumph Center Upsalla
This one probably one of the easiest to use, since it has the OEM part number directly on the fiche page.
Prices are in Swedish Kr.
Triumph MC Parts
Pandora's Motorsports, Tennessee
And one more with OEM parts embedded but also has USD prices
This one has yet another completely different interface - but fairly easy to navigate.
Thanks to Attim for adding this link.
Lings World of Triumph
This one has excellent web layout.
However, they use an internal sku numbering scheme in the actual fiche;
in order to get the OEM part number, place the part in the cart, then click again on the item in the cart, and it will give the OEM part number and description.
Of course in the UK, order directly from WoT
Prices are given in both £ & Eur.
To get US dealer list price, enter that OEM number into BikeBandit.
Probably the best place in US to get OEM parts & accessories mail-order is from MADSS
They are typically -15% off list, free shipping over $40 total order - and no sales tax if not in NJ
Excellent price and service and prompt shipping.
Use either of the sites above to get the part number, then send e-mail to firstname.lastname@example.org
to get price.
Or use the on-line request form - http://www.madss.com/partsrequest.htm
For smaller items, use your local dealer if conveniently located.
Bike Bandit will give good guide to US list prices, however they do not have any way to display OEM Part Number
However if you enter the OEM part # (found by using one of the alternatives listed earlier) it will give you the US price
Go to http://www.bikebandit.com
Note that BB holds no OEM Triumph parts in stock, uses dealer list price (unless you have AMA or similar discount) charges shipping plus CA Sales Tax (if applicable) and is notoriously slow for Triumph shipments.
To check whether a part from another model can be used, utilize one of the fiche sites listed above (e.g. WoT);
find the part for your own bike model and place in the cart;
go to alternative model that you suspect may be same, and locate then add that part to the cart;
if the quantity in the cart doubles, then you know part is same;
however if different, you will see two distinct items in the cart.