Hafler Mono Kit

Nakamichi also made a bridging adapter which will work with the Hafler. The DIY solution is cheap and easy, though. You only need to add an inverting stage to one channel and it can be half of a dual opamp with the other as a unity gain buffer for the uninverted channel.

The DH 200 bridging kits are stored with the hens teeth. They are scarce at best. You may find this rare item occasionally listed on Ebay. That would be your best bet.