I could be wrong on this (often am) but I don’t think any of Harpo’s arrangements have been published with the exception of a piece he wrote titled “Guardian Angel.” Carrol McLaughlin has recorded some of Harpo’s arrangements in cooperation with Bill Marx; she may be the only person authorized to do so.
You may be surprised to know that the company that rents the scripts and music to produce “Animal Crackers” (it was a stage show before it was a movie) will not rent the harp music for Harpo’s solo in the show. They will rent a recording of it so a harpist or someone pretending to play the harp can mime along to the music.
If you want to play as Harpo did, your best bet may be to find a written arrangement of the piece and put your own embellishments into it. Improvisation can be a great learning experience.