For many years, we sold an adapter to allow old home-made photogates and many other odd digital signals to be sent into a LabPro, LabQuest, LabQuest Mini, LabQuest Stream, or LabQuest 2. Unfortunately we no longer make these adapters. The schematic is available if you would like to make your own.
If you have other old photogates around, and you have a CBL-2P adapter, this could be a good starting point for making your own HMP-BTD. We used to build the HMP-BTD by starting with the circuit board for the CBL-2P or the Dual-Photogate adapter for original CBL.