Hello Simon
I have tried, without success, to find a 57th Heavy Field Regiment in either Royal Artillery or Royal Canadian Artillery sites. I have found plenty of units starting with 57th, but after that they are not showing as a Heavy Field Regiment.
You might have better luck if you address your query directly to one of those type of sites instead of here where we are aviation related.
Here is some background data for you:
https://en.wikipedia.org/wiki/Royal_...dian_Artillery
https://en.wikipedia.org/wiki/Royal_Artillery
Good luck in your quest.
Allan