I thought about something after rereading your post on the other thread. I had mentioned in my earlier post on this thread about being a bit late in the season for the winter tires. I was referring to the exact OE "winter version" of your OE performance summer tires.
For example, I have:
Front: Michelin Pilot Sport 4S 275/35/ZR20 (102Y) Extra Load BMW Star Marked OE tire
Rear: Michelin Pilot Sport 4S 285/35/ZR20 (104Y) Extra Load BMW Star Marked OE tire
So my "equivalent" front winters would be the Michelin Pro Alpin A5 275/35/ZR20 (102Y) extra load BMW star marked and my rear winters would be Michelin Pro Alpin A5 285/35/ZR20 (104Y) extra load BMW star marked. These are definitely not available anywhere now for the 15 minutes I spent looking. Neither is the exact tire without the BMW star mark. But, if I start playing with the speed and load ratings, I can find winter versions (that are obviously not star marked), but probably sufficient for winter tires. For example, I can find the above referenced winter tire sizes with a "W" rating (168 mph rated vs. the 189 mph "Y" rated tire). Again, this is probably sufficient for most people as a winter tire for normal street use purposes during colder temperatures. How much to vary, if at all, is based on your comfort. I certainly wouldn't go any less than W if you decide to go this route though. I'm generally risk averse, so I don't generally like playing with these parameters personally unless I have no other choice (i.e. my exact tires aren't available, like the position you're in now), but many do. Also, you can play with load ratings. My OE is 104 load rated, so 2000 pounds/tire. Some people will drop down one load rating to 103 (1939 pounds/tire). If I do that, I can start to see more search results. If you have OE Pirellis, you can do the same with the winter "equivalents" (SottoZero) of the summer performance tire.
I know you're running 19s now, so your numbers are different obviously. I just used mine to illustrate the point because I'm more familiar with mine (this is my second M5 with 706Ms). You can do the same thing though with your numbers off the sidewall.
If you're using the major tire sites, and shopping by car (as opposed to tire size), you wont see these variations; those automated systems, even when you select your trim level and wheel option, will almost always show only the tires with exactly the speed and load ratings ratings of the OE tire selected (and size, of course). Here's a cogent and well organized resource that lists the codes corresponding to the markings below. You may be very tire savvy, and this may be too rudimentary for you if so, but I always like to reference this when looking at any tires for my cars that aren't manufacturer's OE tires. If you start searching by size and seeing what happens if you drop in the tire's other ratings, you'll probably start to see more options. I would absolutely never do this for summer performance tires — star marked OE all the way; I drive this car hard — but it may be an option for colder months.
EDIT — Also, try this: go to TireRack from this link:
https://m.tirerack.com/content/tirer.../homepage.html, click shop tires, then click shop by tire size, pop in your width/ratio/diameter. See if you get more results that way for your size — I did for mine. However, they are only showing Vredestein, definitely no Michelin or Pirelli. But a lot of members here use them as their winter setup without issues.