How could I improve extraction and yield more coffee when brewing with a filter? By my estimate 1 pound of course ground coffee leaves about 900 grams of concentrate in the wet grounds after filtering.
In a perfect world with 100% extraction we could get about 54 cups of coffee from a pound of coffee. Using a drip filter I only get 28 cups.
Using a modified salad spinner I retrieved about 142g more per pound or enough concentrate to make about 4 cups of coffee which is an increased yield of about 13%.
Has anyone found other methods of retrieving the wasted concentrate? I'm thinking something like a press or high speed centrifugal filter.
We need more information to give you good answers. The current question is rather vague and open-ended. 

Is your end goal brewed coffee or concentrate? For yourself or as a commercial product? Is quality (taste) a primary consideration or are you concentrating on yield and/or caffeine and don't care much about taste? You should also describe your brew method in detail, tell us how you are grinding your coffee, how much coffee and water you use (brew ratio) and if you measure it, TDS (total dissolved solids).

You are almost certain to degrade quality if you press or "spin" your grounds to increase yield. If you proceed anyway, a centrifuge is more likely to both produce a better product and maximize yield. Pressing grounds will over-extract and create a bitter result.

You might want to consider brewing espresso, rather than coffee if yield is important. Better quality espresso machines will have quite dry pucks (grounds) and you have the advantage of a concentrated product, if that is a goal. Otherwise you can just add hot water to make an Americano or Long black which is an end product quite similar to brewed coffee but with the higher yield you desire.

Assuming that taste is important and it is to some degree for most people, then you have to consider the detrimental effect that pressing or centrifuging wet grounds will have on taste.