In general, Customs bayonets are less common than their Polizei counterparts but I assure you they existed.

I own 2 clamshells both are shorter blade examples. One of them,a WKC with stiletto blade, could have been a Weimar produced piece but it was private purchased and with no grip emblem, there was nothing to modify during the 3R.

The other is a very short blade with aluminum hilt by Clemen & Jung, a variant identified by Ron Weinand and Gary Walker in their excellent book “Clamshells & Other German Bayonets”.

GDC Gold Badge #290
GDC Silver Badge #310