I have not seen them sold separately, though that doesn't mean that they aren't. But they would be relatively simple to add from some 2-part epoxy putty or similar medium. Especially the enlisted ranks’ Feldmütze, aka Krätzchen. Have you thought about that, or is it not something you're interested in tackling?

Prost!
Brad

You might try asking over at Hyperscale's Tank Talk: https://www.tapatalk.com/groups/hyperscale/tank-talk-f409173/

Does Hornet make heads of WWI Germans? I didn't know.

If you do go over to Hyperscale, you might as well ask in their figure forum while you're there, too.

Prost!
Brad

Hornet and Jon Smith Modellbau both do German WWI heads but no field caps on their own. JSM do lots of German WWI equipment in 54mm including many different types of helmet but no field caps. The ICM 1/35 German WWI equipment sets include helmets but no field caps. The old Scale Link range also has lots of equipment accessories in 54mm but no field caps.

I think you will either have to use helmets instead or resort to sculpting (or scalping Hornet/JSM heads....).

I appear to be a bit late on this.
The ICM WWI German MG08 Team (No. 35711) has both soft caps and helmets as separate items.
The following review has photos of the various sprues:-
https://www.detailscaleview.com/2020/04/icm-135-wwi-german-mg-08-mg-team-35711.html
Hope that's of some use.

Cheers,
Andrew

Now that's good info Andrew, didn't think to look at that set. ICM always supplies the headgear separate from the rest of the head......