It's not so difficult if you look at the numbers.
Moving from 30% to 50% Fat in the diet means increasing fat by 20%. For an average 2,250 calorie daily energy requirement that means an extra 450 calories.
That comes out at approx 50g, or one and a half ounces, of fat per day. The fat could just as easily come from vegetable sources rather than meat, so long as it was either saturated such as coconut or palm, mono-unsaturated such as olive, or balanced Omega6/omega3.
I know in Ireland alone there is approx 60k tonnes of "waste" beef tallow produced every year that is currently fed back into the livestock food chain or treated as waste because there is no market for "evil saturated fats".
Fifty years ago this would have been used to fry bread on a winters morning.
Dividing this up among the four million inhabitants gives approx 45g a day of tallow, which makes up the fat deficit without any difficulty whatsoever.

Equally large amounts of fat are being disposed of in the chicken processing business. (Skinless chicken breasts..aaargh!)
The numbers in other countries are not so different I'm sure.

Ask the average butcher what volumes of fat get trimmed and binned when cuts are being prepared for the fat-phobic modern consumer, and you will get another huge number.
How much fat is collected under the grills of modern "healthily eating" consumers and dumped in the waste bin. How much of the delicious fat in boiled cuts of bacon is trimmed off and dumped before carving.

Once the Fat-is-Evil mindset is changed the fat will be found where it was always, except now it will be eaten, not dumped.