G'day tzeggy14,
As far as I can find out, this was a part that was made for Greenfield - they fitted their own tank and mounting bracket. That was probably because the Briggs OEM tank for this engine model only held 3 US Quarts [~2.8L].
The parts list we have for this model isn't a very clear image, so I can't really say if the Greenfield part number is GT 7002 or GT 7082.
Greenfield themselves would know, and just possibly might have a tank. This mower would be around 1988-92 vintage, so it's getting on a bit.
What's the problem with the existing tank?