There are issues that I see:
Your candidate potentially receives from you otherwise non-public information and therefore has an unfair advantage over any other person bidding on the job. Maybe this is not a big deal in commercial procurements, but in government procurements, this is a definite problem.
If your candidate does not take a reduction in profit or overall fee, then your finder's fee will be added to the cost of the new supplier and your customer is potentially paying more for services than otherwise necessary if it had been a fair and open competition.
Overall, it would seem to be something of a breech of trust, since you are technically working for your client, but potentially influencing a procurement of theirs where you have a financial interest.
The simplest solution to the dilemma is, of course, full and open disclosure to your client about your potential conflict of interest and your financial stake in the decision process. If your client is OK with this type of arrangement, then so be it. If you choose not to disclose, then when the client finds out, he may wonder about the fairness of the decision and whether you were looking out for his interests or yours, while being in his employ.
TTFN