Like kentdep said, make your own. if it's THAT important to have that or any other particular configuration why not stop waiting for what may not happen for a long time, if ever, and get it done? Change out a few parts and you've got it.
I was waiting for a 5 1/2" Acusport Single Six too and well...
If you want one like the ones that Acusport makes but can't locate or if they are, like the one above, not even on the radar it isn't to hard to get one made up like you want it. I have traded off the standard parts in the one above and the one higher up I sold the stock parts to off set the cost of one of these conversions.
Here is my formula for a 5.5" stainless 44 mag bisley:
1) Spend 6 months accumulating a set of stainless bisley parts.
2) Wait a year, until a GP100 shows up on Gunbroker with a cracked cylinder.
3) send the GP100 to Ruger's fantastic customer service department, who replaces it with a 5.5" stainless Super Blackhawk.
4) assemble the perfect 44 magnum, since I like fluted cylinders on six shots anyway..
I'd post pics, but this plan just came together last week and I'm still filing.
Lets just say for what I paid for the broken GP100 and the stainless bisley parts, is less than MSRP for the finished piece.
One of my local shops has a used 5.5-inch Stainless Super Blachawk and I have molested it quite a few times thinking about converting it. They have just been asking too much for a used gun or it would already be in my safe... well that and I keep finding other things to buy