The Iltis rim is 5 x 112mm. There are websites where you can look at the interchange, such as here:
https://sizemywheels.com/lz-pcd/5-112
You may not get a 16" wheel, but since it is just a trailer, a smaller tire would be kind of like a hide-a-spare.
I have one or two spare Iltis rims kicking around the yard. Thanks to a late snowstorm they are all buried under the snow. I could let you have one cheap but the postage might be a little heavy.