As per usual, it appears that a Glowforge design decision has pigeonholed everyone.
Barring your external fan solution, and focusing on replacing the factory fan, the issue is matching the designed airflow balance with a fan that works with the control system. The intake and exhaust fans are balanced in a way to create a negative airflow inside the unit. This reduces the amount of noxious gasses that will leak out of the non-airtight seams. The gaps are all over the Glowforge, not just the door.
There are several required specifications for the fan:
-
Airflow: >= 182.4 CFM @ 13,000 RPM
This is required to maintain the negative interior pressure. The airflow can be higher that this, but the RPM must be exactly this (see below). -
Physical Size: 92mm x 92mm x <= 38mm
This is the mounting size for the existing fan. I don’t have a Pro, so I am assuming if it is thicker than 38mm it may not fit with thermoelectric cooler heatsink. -
Electrical: 12 VDC, PWM speed control, x2 tachometer output
These are required as they match the existing electrical and control interfaces. Note that currently the GF control system simply sets the PWM input to the fan at 100% (full speed). -
RPM: 13,000
The Glowforge control system will set the fan at maximum speed, and will expect to see the tachometer output a ~26 kHz square wave. They are definitely monitoring this and sending this value as part of their telemetry, but I don’t know if they currently alert the user or halt printing if there is a problem*.
The reason why I say they pigeonholed everyone is because there is exactly one manufacturer (at least the only one I can find) with exactly one part number that matches these specifications, and that is the Sunon PF92381BX-000U-S99 (datasheet). Which, as you have noticed, doesn’t currently seem to be stocked any place where it can be purchased in single quantities. A single source with a single product doesn’t exactly give you a lot of choices when it comes to availability of alternatives.
*Since you are running without the fan in place, makes me think they are not halting prints on exhaust fan failures. I haven’t been keeping up on the product announcements or the updates to the firmware (I haven’t worked on this project in quite some time), so I may have missed a notice about fan alarms (other than this one). And, of course, because it works for you now doesn’t mean they won’t release a firmware update (without advance notice, of course) that will stop it from working and leave you dead in the water.