You really don't want someone else building your loop. You may be somewhat apprehensive, that is to be expected but don't let that stop you. Read the stickies herehttp://www.tomshardware.com/forum/277130-29-read-first-watercooling-sticky
and at other forums. If you follow the steps correctly, you really can't mess things up too bad.
The basic problem with having someone else do your loop is, you still have to fill and then leak test it before you can fire up your machine...
My $0.02 - BTW, to answer your question, I am not aware of any websites/shops that perform that type of service - if you're local to a college, you may be able to find someone there who's able to help.