I would expect to come across some wentworth on your bike. Most of the time you can get a 12 point socket to get it. I replaced most of the fasteners on mine with stainless.
Some good vendors would be
MAP cycles
British Only (easy online ordering here)
Baxter Cycle
All of these places are reputable. Avoid the seller listed on the sticky at the top of the forum. Just remember though there may be a cheaper taiwaniese or chinese part available you are better off buying a quality US or UK made part. Trust me on this.
I would also recommend that you get a workshop manual and parts manual. Very good diagrams and easy to find part numbers. Copies can be had on Ebay for pretty cheap.
Good luck
