Hello Andy, and welcome to the forum. Thank you for posting the information about your grandfather. For a glimpse as to what your grandfather endured deeper understanding of the history of the Polish 2nd Corps I highly recommend that you read “An Army in Exile: The Story of the Second Polish Corps” by General Władysław Anders. It is essential reading.
Finding cross # 35845 will be the proverbial needle in a haystack as 50,000 of these crosses were issued, but don’t give up!