I'm sure you know you can only get them used, Shark does not provide major parts and the Chinese have not knocked-off parts from the older models (yet).
There was 3 of them here, but they sold out in October. I'd just keep an eye out.
https://www.ebay.com/itm/333563652533
If you are really desperate or need it done right away - as a last resort you might just have to buy the entire base unit of the vacuum ($49) to get the brushroll. Then you can strip that down and sell the rest of the unneeded parts off to get some money back on the purchase price at least.
https://www.ebay.com/itm/Shark-Motorized-Floor-Nozzle-Motor-Chassis-for-Navigator-NV105-Vacuums/254802250187
Good luck!