It's only the silver versions of the HD DA Limiteds that are being discontinued. The silver 15mm was discontinued a while ago and the lack one still exists. Now the same is happening with the 21mm. If you look at the Pentax site they are still both shown as current lenses.
????? / K??????? / ??? / ?? | RICOH IMAGING
But if you go to the store, the silver versions are marked as "Outlet".
DA?APS-C??? - K??????? - ??? | RICOH IMAGING
I think this misunderstanding comes from Pentax Rumors. They are reporting the very old news of the black SMC version's discontinuation as if it is the current HD version. That site is very slopping with fact checking.
I'm not going to link to the Pentax Rumors article, but the more credible report from Japan that this probably came from is here.
HD PENTAX-DA 21mm F3.2AL Limited ???????????? - ???? ???????
It's worth mentioning that silver versions of Pentax lenses have often had limited runs, including the silver versions of the SMC versions of the same lenses. This is not unusual, and just means you have to hurry if you specifically want a silver one.
---------- Post added 05-28-23 at 09:05 AM ----------
Further evidence that they don't intend to discontinue the black lens any time soon is that they just launched the K-3 III Monochrome and included this lens in all the promo shots.