Physics teachers seem to lack such platform; has there been any effort to create something like physicseducators (or a more general scienceeducators) stackexchange?
There were two previous attempts at creating a Science Educators site, which would have covered physics, and both attempts failed and were deleted:
As posted on the Area51 FAQ:
Deleted proposals can be re-proposed anew by users with renewed energy and, hopefully, better resources to bring it to commitment.
So there really wouldn't be any problems to re-re-propose the site in terms of SE policies, but the concerns of participation may still exist.
If you could access the deleted proposals, you could see what did and did not work, thereby making a better future site. I don't know if this is possible currently.
Come here to the PSE and try to lobby for making it ontopic. The chances are nearly negligible in the short term, but a little shift can be reached if you do it long. I will try to help, but my effect alone is very little.
You can get a lot of deleted SE content from the https://archive.org , the last snapshots of the (in my opinion, purposelessly destroyed) proposals are these:
You can also recreate the proposal on the Area51, import the most upvoted questions there, I will help if I can. The chances are low also on this way, but you can significantly increase it if you try to collect support on the meta sites and in the chatrooms.
My suggestion would be to create a science educators site, which would integrate at least biology, chemistry and physics (maybe some engineering, too). On this way, you might get help from the communities of all the relevant sites.
Note, the A51 shows a linearly decreasing tendency to create new sites since some years. My extrapolation is that it will stop working around at 2020. Probably not even the SE has any idea, what to do with it, but the general attitude of the community is very well visible below that MSE post.
A third possibility would be to somehow politely ask some already existing educator site to extend its topic. Unfortunately, the major problem is that most SE communities become itchy if there is any suggestion about the extension of their topic, but they get very excited if there is a way to narrow it. :-(
However, small sites are lesser exclusionist, and both the matheducator and the cseducator are small.