In a way, the answer is Yes. Although, I would not consider any of the sites where you would get the ROM from to be "official".
What you need to do is download ODIN3 (or hemidal) and use that tool to flash the Stock ROM on the device. Doing so will most likely require you to completely wipe the device to factory state.
I found a couple sites that do have the Stock Firmware, but I don't want to link to the ROM directly for a couple reasons. One, I don't know the legality of linking to a the Stock Firmware and if the file is no longer valid in the future, I do not want this post to be "out of date".
If you google "flash i9000 odin stock" you will likely find a couple different sources that have the files needed to flash back stock. When I did this, the first site had the 2.3 XXJVU release for the i9000, and the .pit file (which is also required when going back to stock, and the drivers. It also is a tutorial on how to flash it.