First of all, I really admire you for your effort! I'm guessing it must not have been easy. While I do not have any personal experiences to share, I found this article that you may find useful: http://exclusivepumping.com/sample-pumping-schedules/ It offers a sample pumping schedule that may help sustain your supply (see the second section for schedule for older babies). Also, I've read that the usual suggestions to increase supply also applies for exclusive pumping mummies. For example, pumping more frequently, drinking plenty of fluid and having a balanced diet, plenty of rest, and trying supplements such as fenugreek and oatmeal etc. Hang in there and hope you find something that worked. Long term pumping is possible (from what I've gathered over the internet). Take care!!
Just to share, for my first kid I did exclusive pumping because she just wouldn't latch. I manage to pump till she's 10months. My milk supply did drop as weeks/days go by nearing the end of 9months. For my second kid, I manage to latch him till he's 15months. And still having ample supply of breastmilk. Pumping milk out will not be effective as baby latching, when emptying the milk from the breast. So I guess that by pumping, the milk is not totally emptied from breast and therefore our body doesn't produce as much milk like from the beginning.
I did exclusive pumping for 1 year +, my supply didn’t stop for the year. Healthy diet and lots of water helps in maintaining the supply. And fish. I pump every 4 hour.
I was exclusive pumping for my first Lo and it lasted 9mo.