You could try bison fat, although I believe bison are, on average, less fatty than other cattle. The USDA (United States Department of Agriculture) forbids the use of hormones and antibiotics in farm-raised bison:
Q: Can hormones and antibiotics be used in bison raising?
A: Antibiotics and growth hormones are not given to bison.
Ahhh... But not in USA. It will be full of "get fatter" hormones(?)
I am not sure organically grown beef fat is available, or as cheep.
Where I live, where it is illegal to feed grow drugs to cattle, I do a lot of cooking with beef fat.