Well, you may not have to substitute at all. I just found the success incense on Google. It's cheap too. Here's a link:
http://www.merlinsdreamshop.com/catalog ... cts_id=189
Sorry, I should have looked for that before. Also, if you don't want to buy it, or don't have time before you do the spell, maybe you could just get some incense that you like, and bless it and charge it as "success" incense. Just put success energy into it (or however you personally charge things) and concentrate on the idea that when you use that particular incense, it will help your goals become reality and bring you the success you desire. I can't imagine what is so special about the "success incense" they sell online, besides the fact that it says "Success Incense" right on the bottle. So I'm sure you could just create your own if you desire. It is the thought and energy behind a spell that has the most powerful effect, in my opinion. I actually believe that the thought and energy alone are enough, and that you don't need the actual spell. The spell is mainly to help promote the energy behind your thoughts and make you believe that your wish is going to come true. It's New-Agey to say that, but it's what I believe is true. I think prayer works the same way. The thought behind it is what makes it manifest.