One thing I was told a couple of weeks ago is that everything should start becoming more available starting the end of February. Take it with a huge grain of salt. I have seen where Winchester has a new temp stable powder that I didn't see load data for less than two weeks ago but it is there now. This means that there is a slight chance that availability could be improving soon.
At this point I suspect that they are filling backorders and don't have the excess capacity to make the TNT. Depending on how their production lines are set up, it it likely that 277 bullets are built on the same line as 30 cal. Unless they have committed to fill a particular order of ammo with the 90 grain TNT, they will be producing whatever they make the most money on and can run without having to retool the production line.
Every time they switch to make another bullet, they lose a lot of time changing out tooling and verifying that all the machines are producing in-spec product. This reduces the total bullet output and profit. They make the most money running the 308 and 223 bullets continuously until the market is saturated.
I once worked for factory that got a new manager who saw a bunch of old machines sitting idle and decided to sell them. He reasoned that we could just switch the tooling on the remaining machines when needed. He did not understand the huge amount of lost production every time a tooling switch was made and we soon were unable to fulfill a significant number of orders. Those old machine sat idle a lot of the time, but they were set up and ready to start production almost immediately. Because we made so many different products, our productivity dropped dramatically when we tried to retool machines much more frequently. Within a year, that factory was shut down.