Actually, in the past year or so of the "shortage", I've seen more 357SIG on the shelves than I have .45acp. At both Walmarts around here, it was about the only pistol caliber on the shelves for months. Its readily available on the web too. Its also cheaper than .45acp..45 acp is plentiful compared to the .357 Sig.
There are a couple gun stores near me that have almost every caliber and configuration. So that is not a problem.