Available June 10:
Presto (https://www.prestomusic.com/classical/products/9328997--selim-palmgren-complete-piano-works-vol-5)
Amazon UK (https://www.amazon.co.uk/Palmgren-Piano-Works-Jouni-Somero/dp/B09YVK4X5N/ref=sr_1_1?crid=LXVTNP08Y8K1&keywords=palmgren+piano+5&qid=1654644469&s=music&sprefix=palmgren+piano+5%2Cpopular%2C226&sr=1-1)
Amazon USA (https://smile.amazon.com/Complete-Piano-Works-Palmgren-Somero/dp/B09YVK4X5N/ref=sr_1_2?crid=31KDZF3B82KD3&keywords=palmgren+piano&qid=1654644103&s=music&sprefix=palmgren+piano%2Cclassical%2C173&sr=1-2)
(https://i.ibb.co/DCVGd4k/81pjb6p-Nvj-L-SL1500.jpg)
(https://i.ibb.co/fX3f34p/71-Z4-Gu-B3y-SL-SL1200.jpg)
...and looking at his list of works for the piano I reckon there are at least another five volumes.