I have no idea about the stacking compatibilty of the mk1 and mk2 cabs, but I did find a MK1 mbe 210 (says its still on stock on the site, maybe worth sending an email)
http://www.effectpowersupplies.com/gallien-krueger-210mbe-2x10-bass-cabinet-1701-p.asp
hope that helps in your search.