Hi,
try contacting these guys
http://www.emchire.co.uk/
according to
http://www.emchire.co.uk/S01.HTM
they have the R4131D driver, but don't say what language to work with, so I'm assuming a .dll which can be called from CVI or LV. They hire out EMC equipment, but you might be able to beg drivers from them?
Having said that, writing a driver for CVI or LV shouldn't be that difficult if you have the manuals for the hardware. Concentrate on the functions you need first, and you can always expand it later, even posting it back to the NI website so others can share in your work!
Hope that helps
S.
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