I have no computer for you to operate and I have no computers for you to operation.
Where you wrote "operation" above, I guess it was a typo — it should be "operate."
Both sentences are correct, but while the first one presupposes that "you" only needs one computer to operate, the second one may imply that "you" needs more than one computer, or that there are no computers out of which one could be assigned to the operator.
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