The only place I can think of that MIGHT do this sort of work is
mac-res-q -- they do repair work and might do installation. The video card is tricky. You can find them on eBay and once in a while a reseller will have some in stock. They are a bit shorter than the standard cards and are not being manufactured any more.
cubeowner.com is a good place to monitor for Cube parts, they recently posted a note about availability of video cards at a reseller (check the "Buy stuff" section).
Another option would be to find a local Mac reseller and see if they would do an installation. Sonnet recommends professional installation for their CPU upgrade so there must be people out there doing them.