Welcome to the forum, of compact utility tractors. May not be the place that feels comfortable giving you advice on a 'big' tractor.
But, don't give up hope. There are a lot of knowledgable members, and one may just have the answer to your question.
I can't tell what your ideas are for a 'larger' pump. One that is PTO driven and max's out the HP of the 4020 tractor as being the limitation, or a pump that is a replacement of the OEM pump on the 4020 now, but just more gal/min?
If any suggestion, I would say go to your Deere dealer or go to a hydraulic pump manufacturer.
If you can feed us more information, maybe someone will pick up on the thread and help you with a solution. /forums/images/graemlins/wink.gif