For the H/L, Silvania Silverstars work great. I replaced mine with the standard wattage and it makes a huge difference. Others have gone brighter, too.
Sites? There a bunch. There isn't too much B4-specific stuff out there anymore, though. For just general parts and accessories, I like the Dennis Kirk catalog. Their
web page is a mess, though. Being the antisocial guy that I am, I find what I want in their catalog and then order it online so I don't have to talk to anyone.