mg load cell?

Anyone here know of a source of milligram scale load cells (actually they would probably be strain gauge based load cells)?

I am working on a project that involves data logging very small changes in weight. Think of a beaker with fluid, where I need to measure/data- log and download to a PC: weight and temp. I have plenty of data logging apparatuses for temp, humidity, weight (large scale though) etc...but nothing anywhere close to milligram levels.

Any other ideas as to how I could measure changes over time in a unit this small?

Thanks,

Phill