You can find a physical copy of the book in the ETH-Bibliothek Zürich
It is the second edition and was printed 1773 in London.
The book has additional comments
A download link is available at ETH e-rara (https://www.e-rara.ch/zut/content/titleinfo/2853134); and on the gallica website (https://gallica.bnf.fr/ark:/12148/bpt6k987925/f2.item.r=a%20dissertation%20on%20oriental%20gardening)
You can find a full copy of the book online on archive.org as well. https://archive.org/details/gri_dissertation00cham/page/n45/mode/2up