I've dug around a little and been unable to work out if the SSV code for releases of Matrix prior to 3.28 will be released as GPL.
In particular, I'm interested in adding SOAP support to an existing 3.22 GPL install.
Apologies in advance if I've failed to read things through properly.
In 3.28.0, the licence was changed for that code. Previous versions still retain the licence they were released under, SSV in the case of SOAP.
So no, there is no GPL version of the SOAP package for 3.22. You'll need to first upgrade to 3.28.0 and then install it OR take the 3.28 version and adapt it for 3.22 (I don't advise this because it probably wont work at all, but it is your other option for GPL code).