"We have made the difficult decision to no longer supply forums and FaceBook groups with discount codes. Our discount program for repeat customers is still running though. We will send a discount code via email approximately one month after an order is placed (each time!). Those codes can be used and shared as many times as you like until they expire.
Just an idea.
Instead of removing the forum might it be revisited in some form where members can keep it current with their personal discount code so that fellow members have access to the saving?