I can give you some ideas for a repair if you can not buy just a mount.
Dash cam mounts are almost always made of ABS plastic.
ABS plastic melts in acetone. You could try covering the 2 ends of the broken parts in acetone to soften the plastic so it will join together. It may or may not work.
Fingernail polish remover can be found that is non-acetone but you would want 100% acetone fingernail polish remover that is available for around $1 for a 6 ounce bottle. You can buy abs filament like this.
https://www.ebay.com/itm/362414436211 and snip it into short sections place it into a closed jar of acetone and melt the plastic into a liquid you can paint on for a repair. This is a slow and tedious process that may or may not work. My first attempt at joining 2 parts together this way saw the part break in half when placed under mechanical stress.
A better solution if you have a dremel is to cut the abs filament (in the link above) into short sections maybe 2-3" long.,Put that into a dremel at medium to high speed and let friction weld the pieces together. This friction welded repair should be as strong as the original part was from the factory. Factories use friction welding in automobile production.
The easiest solution requiring the least skill is to get some epoxy rated to handle plastic and epoxy the mount back together. I have read that superglue can also work BUT superglue creates a brittle bond that might not hold up under stress.
I have used both the paint on liquified ABS and epoxy to fix a mount. I believe using the correct epoxy for the job makes the strongest most reliable bond because tehre is little elft to chance. Welding the parts together by using ABS filiment should create a very strong repair but I have not tried this method of plastic welding myself.
Do NOT use PLA plastic for the repair. Insist on obtaining ABS plastic. PLA plastic will crack inside a hot car. ABS is much more stable in the heat found in a hot car in the summer.
