Hi Greg,
Thanks for your reply. I understand that the cabs are tuned to the speakers spec and this is one thing i would kind of been worried about. I used to use a 4x12 that had a mix of celestions and eminence speakers in it. I didn't notice any discernable difference but then again, I didn't know the speakers where different until id owned it for a few years so I didn't really know much difference with it.
As for where I found it, it was on thomann, I'll post the link below. Available immediately too.
http://www.thomann.de/gb/hartke_10_ersatzlautsprecher.htm
Hope that helps your friend