As already stated above, I don't think that there is a cable that does that kind of conversion. I use a Monarchy Audio DIP for that purpose. It also reclocks and boosts the digital signal, and offers AES/EBU input/output as well. I think that there are some less expensive products that will convert toslink to SPDIF, but I don't know how well they work.
You would be better off using SPDIF from the beginning, and once you add in the cost of the converter, and a good toslink cable (required, a super cheap toslink cable sounds terrible), you might have been able to get something that offers spdif output on it's own, or at least be well on your way.
-Aaron.