Your only option if you don’t want 8, but 6 or 7 instead, is to try and find a retailer - most likely an on-line one - who has a few older versions left.
There is a chance that Steinberg may forbid anything sold but the latest version now.
But the above advice worked for me.
Just when Cubase 7 came out, I bought Cubase 6 on-line for a discounted price which even included the full HALion version - a $350 value - and also got a free up grade to 7.