http://kgparts.com/index.php?page=kgfuel
http://www.skernracing.com/fuelrails.html
I've made my own and used a few different aftermarket rails. If you haven't made them before just buy them pre-made and save yourself some headaches.
Summit and Jegs are hard to beat on their -AN prices. Their house brands are less expensive but I have had issues with the Summit brand leaking. I'll usually pay the markup and stick with Earl's because I know I'm getting a quality part.
With the S4/5 you can have the Bosch injectors setup with a pintle cap that allows them to fit in the stock manifold without the need for sleeves or a wad of o-rings to get them to seal correctly. Marren sells these injectors as their "Pro-Import" injectors at a serious markup. If you have a competent injection shop close by you can take a regular "domestic" Bosch EV1 injector and have the pintle cap changed to replicate the Denso injector for a stock fit with the stock injector grommets.