Here are some links to pages that will fill any gaps that you may have. There are two vendors and the madass owners forum. I  can personally recommend MadassArmy to anyone as your first stop, as a regular user myself!

MadassArmy is a global online community. Its THE meeting ground for all things Madass, from small modifications and upgrades to general discussions and even full overhaul projects. From the UK to NewZealand, madass owners all over the world meet here. Almost 99% of answers to any madass question are just a click away. Be sure to show your pride and order your MadassArmy stickers today! Click on image to be taken to the site.

Smack bang in the middle of Harley country you will find this small company that has been long established as the US  home of the Madass. Although they may not have a vast catalogue of parts, they are extremely knowledgeable and friendly team who have sold more madasses than any other retailer in the US. 

These guys are Atlantic side too, but offer some of the most competitive prices on OEM parts you will find. More business focused than last year could see them gain popularity in the madass market. Currently however they do not seem to be shipping to the UK. Edit: This link works fine now, thanks to those who pointed the fault!