The part number of the bracket from Weber rotisserie kit #9890 is 98100 (you can "see" this part at ereplacementparts.com).
The problem is that this part has been discontinued and is not available new anymore (ereplacementparts had a limited stock earlier this summer but not any longer).
Onegrill lists the bracket for $10+shipping if you search for [URL="https://www.onegrill.com/Motor_Bracket_for_Weber_Grills_p/4pb
However, it's not cost effective to buy these parts piece by piece. You'll have a better chance finding a new old stock kit or a used complete setup with the motor and the bracket. I've come across 2-3 sets this summer for about $20 locally.