Quick search found this https://www.amazon.com/Pilot-Kneeboard-Aluminum-Clipboard-Compatible/dp/B07YFQ3G7C/ref=mp_s_a_1_2_sspa?crid=1UUX6KYBVGVKN

Never used it, but maybe it will work for you.

The other option getting an iPad window mount and then you can have the paper on your knee.