Ammunition and guns for the cartridge are still in production. In fact, it seems to have seen an uptick in interest over the last year or so.
Right now, ammo is scarce all around. Ammunition companies are doing triage. .223, 9mm, .40 S&W and the big-demand cartridges are going to be given priority in production for the near future. This may result in a temporary shortage for the 5.7x28.
In the depth of winter I finally learned that there was in me an invincible summer.