The contractible complexes are all given in HAP-readable format. To access the information copy the files to GAP-DIRECTORY/pkg/Hap1.11/lib/Perturbations/Gcomplexes/. 
After loading HAP you may then use the command "ContractibleGcomplex("filename")" to construct the desired non-free resolution in GAP/HAP.

The files labeled "GL2OdHAP" contain contractible complexes for the general linear groups of degree 2 over the integers of the real quadratic number field Q(sqrt(d)).

In the cases where the class number of the ring of integers is greater than one there are two files named GL2OdSteinitz1HAP and GL2OdSteinitz2HAP the former containing a 
complex for GL2 over the integers of Q(sqrt(d)), the latter a complex for the GL(L) where L represents the other isomorphism class of modules of dimension 2.