Hi newcomer and welcome to the Tom's hardware forum.
As kaosnkorruption says MSI has the only one mobo AM3/DDR2 but the price of this is more that an AM3 mobo plus DDR3 so is better that u get an AM2+ mobo that support both DDR2 and AM3 without problems.
Here are two options that can works for ur rig.
1- ASUS M4A77D
2- MSI 790XT-G45