Here is the link to the pump output adapter: http://www.coralvue.com/extreme-skimmer-input-adapters
Your skimmer likely was the Extreme XS 200 if the PSK2500 was mounted to the side of the pump.
We have a whole assortment of plumbing parts on our website. I believe this is the adapter fitting you are looking for: http://www.coralvue.com/metric-to-imperial-pvc-adapters