What's a good Free-Moving Backpack PC Alternative?

We have started development on a VR experience project using UE4. We have 2 months to finish it, and have been developing for our own Backpack PC. However, now that the deadline is closing in, someone on the team reported that backpack PCs just aren't widely available anymore. We can't get backup batteries, and it and I have been told that this completely invalidates our option to use backpack PCs, so we ideally need to find an alternative solution. The space is only 3x4 meters, and we'd need people to move freely around it. If we absolutely cannot find any alternatives, we'd have to switch the whole project to the Quest. Which doesn't seem feasible, since our target platform was PC before, and we'd essentially have to start all over again.
So does anyone have any ideas for alternatives to the Backpack PC, or even if there might be ways to get access to backpack PCs?