look in \data\Cfg for the file Basic.cfg. Scrolling through it reveals:
highlighted in yellow are the rounds of SS shells allocated to the weapon. Currently only your 10.5cm SK C/32 and 8.8cm SK C/35 have starshells. This is assuming of course that SS is the same thing in SH4 as it is in SH3. I rarely play SH4 as I mod SH3.
[AMMO_TYPE0];10.5cm SK C/32
Idx=0
Year=1939
Month=1
AP=40
HE=60
SS=20
Renown=0
[AMMO_TYPE1];8.8cm SK C/35
Idx=1
Year=1939
Month=1
AP=40
HE=160
SS=40
Renown=0
[AMMO_TYPE2];3.7cm FK M 42 Twin
Idx=2
Year=1943
Month=12
AP=1600
AA=2400
Renown=0
[AMMO_TYPE3];3.7cm FK M 42
Idx=3
Year=1943
Month=12
AP=800
AA=1200
Renown=0
[AMMO_TYPE4];3.7cm SK C/30
Idx=4
Year=1939
Month=1
AP=400
AA=800
Renown=0
[AMMO_TYPE5];2cm FK C/38 Flakvierling
Idx=5
Year=1943
Month=5
AP=4000
Renown=0
[AMMO_TYPE6];2cm FK C/30 Flakzwiling
Idx=6
Year=1940
Month=7
AP=2000
Renown=0
[AMMO_TYPE7];2cm FK C/38
Idx=7
Year=1943
Month=1
AP=1000
Renown=0
[AMMO_TYPE8];2cm FK C/30
Idx=8
Year=1939
Month=1
AP=1000
Renown=0
[AMMO_TYPE9];2cm FK C/38 Flakzwiling XXI
Idx=9
Year=1944
Month=4
AP=2000
Renown=0
[AMMO_TYPE10];2cm FK C/38 Flakzwiling
Idx=10
Year=1943
Month=7
AP=2000
Renown=0
Seeing that the SS rounds have a number greater than 0 you should have SS shells. It could be that the SS rounds aren't in the particles.dat file. I will take a quick look. Duh!! I should know it is, I ported your SH4 particles and materials.dat files to SH3

Hmm...let me take a quick look at the shells.dat file for this ID: CC9681C9C15D5456
that is the starshell's shell object ID.
found it. Let's check the shells.sim to make sure it has effects tied to it: yep. Set to detonate at 1800 meters, using effect ID B389E6C2687816AC which in the particles.dat file is the event StarShell. Codewise to make the starshell is there. I would check your guns .sim files to ensure that the starshell's shell ID is located in the correct spot and it's amount is set to a value > 0.
I was bored over in the SH3 forum so I decided to pop over and see what was going on over here
Ok, I was really bored so I checked your \data\Library\USSubParts deck gun .sim files and either they were missing the starshell shell's ID and/or the amount was set to 0. That is one reason (and probably the only reason) why you don't have starshells
Racerboy