Hi There,
I do not know in which part of the world you live, but here in the Netherlands we can purchase steinberg upgrades through online webshop such as www.bax-shop.nl or www.thomann.de. If they do not list the halion upgrade mail them I’m sure there willing to arrange it for you. If you are in the USA then mail something like musician friends or similar (often I get a better price then Steinberg offers!!!)
Good luck with your search,
Menoj