wow thats an amazing find! from what i know most museums in general rely on free donations rather than paying for exhibitions
A computer museum that seems to be currently accepting artifact donations is:
https://www.computermuseumofamerica.org/donate-artifacts/ I didn't see the IBM portable personal computer on their desired items list, but I couldn't seem to see it on their exhibition page so I'm assuming they don't have it? So it might be worth a shot! There are quite a few computer museums in the U.S but not all of them are currently accepting artifact donations.
If your wanting to sell it i'm sure there are computer collectors out there who'd be interested!
there are some forum boards that are dedicated to vintage computers and buying/selling them such as:
https://forum.vcfed.org/ i've also seen many vintage computers sold on ebay
I wish you goodluck! I'm sure there will be someone who wants to give it a good home