Two options.
Option 1:
ws = get_param(gcb,'MaskWSVariables');
ws will be 1-dimensional structure array with fields Name and Value. One element of ws, let's assume it's 6, will have ws(6).Name = 'a'. Then ws(6).Value is the A matrix. Similarly for B, C, and D. If you want to automate that, you'll have to do something like
ws(string({ws.Name})=="a").Value
Option 2:
Use the linearize() command to get the ss model of the block, then use tf if you really want the transfer function representation
sys = tf(linearlize('mdlname','blkpath'))
where mdlname is the name of the Simulink model and blkpath is the full path to the block. Or
sys = tf(linearize(gcs,gcb))
if you have the block in question selected in the Simulink model
