All file can be found here

 

So here is a step by step guide how to create custom system partition in cygwin:

A) Download an shx firmware (for example 1.1.31 T-Mobile HERE)
B) Download SBF Recalc 1.2.9.1 and CG2 (De)packer (version 1.1d or newer)
C) Download and install cygwin (I believe you don't need any extra packages) and yaffs tools.
D) Extract the firmware from the arcive, open the shx in SBF Recalc and press "Split Flash-File".
E) Open the CG2 which was extracted in CG2 (De)packer and split it.
F) Copy the systemsec.mbn from the extracted CG2 into the folder (I suggest renaming it to for example: "systemsec-stock.mbn") in which you extracted the yaffs tools (It must be in cygwin path, so if you istalled cygwin into C:\Cygwin, use for example C:\Cygwin\usr\local\cliq)
G) Open up cygwin and nagivate to that folder (example "cd /usr/local/cliq")
H) Extract the image in cygwin (type for example: "unyaffs systemsec-stock.mbn tmo-system"). If you used stock one, then if will say the image is broken but that is ok, since the tools is not expecting signature.
I) Mod it
J) Pack it back using mkyaffs2image (type for example: "mkyaffs2image tmo-system systemsec.mbn")
K) Put the systemsec.mbn back to the folder where you splitted the CG2 (normally using Windows).
Note: If you get message about no permissions, right click on the systemsec.mbn, hit properties, Security tab and add yourself full control, or set yourself as the owner of the file (cygwin might be buggy here)
L) In the CG2 (De)Packer, press "Open From Folder" and navigate to the folder with splitted CG2.
M) In advanced menu, hit bypass signature.
N) Hit Recalc Checksum. After that systemsec.mbn will be in red and with ID 31 in HEX.
O) Hit Create CG2 (created in rebuilt subfolder of the splitted CG2 folder).
P) Copy the CG2 into the folder you split the shx.
Q) Hit "Open CG-Folder" and navigate to the folder with splitted shx.
R) Hit Recalc checksum.
S) Hit Create SHX or SBF file (created in SHX-Flashfile or SBF-Flashfile subfolder of the splitted shx folder).
T) Flash the file new shx using RSD Lite version 4.5.7 or newer.