I am a user of MRTG and RRDtool for a long time. I also contributed some code to RRDtool and provided some manual pages. Last but not least I have spent and still spend quite some time on the mailing lists. I am also an RRDtool programmer in the sense that I write scripts for others. Like many people I'm hesitant to call myself an expert but I truly believe it is safe for me to do so in the RRDtool case.
You can hire me as a consultant/programmer. Please send me an email describing the project you like me to assist you with. I will contact you for further details.
Please make sure to describe clearly in your email that you want to hire me. This so that your email doesn't get lost in unsollicited email and/or requests for free help (which I redirect to the mailing lists).
You can reach me here. Please include "consultancy" in the subject as well as "rrdtool".