I know there are free digital copies of the Quran in esperanto, but I was wondering if there are any physical copies one can purchase?

To the best of my knowledge (I will accept correction), there has only been one complete Esperanto translation of The Noble Qur'an, under the title 'La Nobla Korano' translated (with Arabic text) by Italo Chiussi (second edition 1970). Its accuracy or acceptability to Muslims I cannot guarantee. It is available online as a PDF, although there are always questions of copyright. For a physical hardcopy, you might try various used book exchanges. I have had good success with Alibris and AbeBooks in North America. As I write, AbeBooks lists a copy from a European dealer, although it might be rather expensive for a North American purchaser.

There's a second translation. It's called "Sankta Kuraano", translated by Muztar Abbasi in 2000. It is more recent than the Chiussi translation, obviously, but I think the Chiussi version is easier to find because it was printed multiple times.