There is an aftermarket unit available, but it costs nearly as much as the OEM (looks the same as the OEM).
Depending on your install you might be able to do something to assuage the problem. After burning our stove for 8 yrs. w/o a fan, I was considering buying a fan unit. We have a corner install, where an old Fisher used to sit. Looking at the clearances, I found I could easily place a small table-top type (6-7") fan on the floor behind the stove. I bought a little 3-speed "Honeywell" for this placement. I then took a piece of snap together stovepipe & cut it a bit to fit & shaped it to roll up into the rear stove cavity -- sort of a 90 degree w/a nice slow corner roll to the metal. That little fan moves considerable air -- maybe not like the OEM unit would, but gets some serious air-flow going. I have purposely over-fired the stove (or almost so), & then turned that fan on high for a bit & the stove cools right down -- so it is very effective in that respect, as well. (Usually run the fan on "low", or needing the heat, on "med". "High" is a bit noisy -- the sheet-metal flashing vibrates some. )