If you are looking for the SG-1 styled vest then your realy only have two options: the Blackhawk Medic/Utility vest or TheVestGuy's Stargate Vest
If you are looing for the SG: Atlantis style vest, then you have a few more options such as: Blackhawk, UTG and Condor. The latter is a near identical match the the Blackhawk version at half the price.
Take a look at the below link to our group's Costume Guides, as the pics and links might help.
SG-Operations Costume Guide
Good luck and feel free to ask any questions that you might have.