Vaibronco: helicopterhelmet.com comes highly recommended by many of my friends. I've only purchased parts from them myself.
If you're going to go through the hassle and expense of shipping the helmet to them for refurbishment - or simply a paint job - I'd consider having them fit a new styro liner. Styrofoam does degrade over time due to a number of environmental factors, and since that's part of the primary impact protection mechanism you may as well refresh it. Also (and especially with the SPH4), I'd recommend fitting a Zetaliner from Oregon Aero as well as their hush kit and ear seal covers. These items make a huge improvement in comfort with that helmet, which means you're more likely to be wearing it should you need it.
That said, I'm sort of a cheap bastidge and am refinishing my SPH5 at home, preferring to spend my money on the comfort upgrades
