Suggestions for hiring sysadmins / programmers for short-term work?

We are looking to hire a sysadmin (perhaps with some programming prowess as well) to help with some general Linux tasks on CentOS; such as resolving issues (various failed dependencies and esoteric error messages) with some third-party software we are trying to use, and other similar headaches beyond my personal expertise.

Ideally I would like to find someone who is available on demand for just a few hours of work or to look at specific issues when they come up. I am aware of sites like Guru, Elance, oDesk, etc and was hoping that maybe the HN crowd had filtered through the best of these.

I tend to do most of my own admin (and programming... and design... and...), but as launch grows closer I am feeling stretched pretty thin.

Thank you for any suggestions in advance!