An SCXI chassis can be cabled up to 10m away from the host PC using a shielded 68 pin cable:
http://digital.ni.com/public.nsf/websearch/B30DF2FE6B6C2E2786256A62005BADE2?OpenDocument
NI does sell a 10m cable - see this webpage:
http://sine.ni.com/nips/cds/view/p/lang/en/nid/11799
The part number for the cable appears to be 184749-10.
Regards,
Logan