I have a Victron Energy MultiPlus 48 volt pcb board which has blown one of the polyester film capacitors. Would anyone know where I can get a replacment?

The logo looks to me like Epcos, but I can't find that part number. My suspicion is that this is something to do with the merger of TDK and Epcos. I'm guessing it's a 2.2 μF 100 V film capacitor.

Something like this should do:

https://www.mouser.co.za/ProductDetail/EPCOS-TDK/B32522C1225K?qs=Rx47eAgti545dYvBXYPn5g%3D%3D

These have 15 mm pin spacing; is that correct? I estimated the length of the capacitor from your photo at 18 mm.

But the postage will cost you more than 6x the price of one of these. You might be able to find a similarly rated film capacitor in a hobbyist shop and it looks like there is plenty of room there in case the size and pin spacing isn't exactly the same.

Of course, the question is: did whatever caused this part to fail also damage anything else? Not every electronic failure is visible.

Is this part across the battery perhaps?

At least Victrons are easy to service; all those through-hole parts. Maybe you can obtain a schematic diagram from Victron, and determine that exact specification for that part.