Hi,
Displaying "Related products" in the Virtuemart Core was problematic in the official VM Component as well, so we have eliminated it from our template as well, but recently they have fixed it (with VM3.0.12). Now, we need to re-add this feature to SportMart, which will be available in the upcoming SportMart version.
FYI: It is not an easy task to achieve, because the whole idea of displaying Related Product has been changed in the VM core. I can't provide you the step-by step guidance here.
Regards.