There are some SD70's up for grabs on http://www.worldoftrainz.com/
but they are all payware and I'm unsure if they are in the CSX livery.
There is word of Sureshot building a CSX SD70ACe I think it is, but it won't be finished for a while, check out Frank McCall's website on http://www.trainzstation.com/Files.html
To be honest I think it is a case of look at all American 3rd Party websites for specific CSX locos, as most of the ones I've downloaded from cover all major American railroad companies and CSX stuff are mainly Geeps, Dash 9's and SD40's, etc.
Sureshot's CSX reskin of Frank's SD70ACe is now available from Checkrail.com - click here.
The download does NOT include any dependencies, AFAIK everything required is available either from the DLS or from other similar locos at TrainStation.
If anything is particularly elusive let me know and I will chase it down...