Nice find! In their prime, Hercules made some very good bikes. They were a worthy competitor to Raleigh and Rudge.
There are a lot of parts resources in the UK...some of the EBay ones have lots of good bits at what seem like decent prices.
Check out the aforementioned web site. He is a collector, and has a lot of good resources.
Also, The Old Bicycle Co and Cycles of Yesteryear stock older parts online. They are worth the time to send an e-mail.

Keep us posted as to your progress. There is a growing base of enthusiasts for Roadster bicycles here in the US.
Clubs are even starting to spring up, for the first time in decades. I myself love this stuff.

Corey K