When we started using Indesign for our mag, we used Caslon, but now we can't access it. I want a similar font for our headings which was Caslon italic swash especially, as I liked the swirl on the top of the B serif etc.

I am a home producer and find it all confusing. Can we buy it as a one off for myself and my sub editor, only 400 copies twice a year. A charity so not much money. Is there a suitable option?

You should probably take a look at Google's Libre Caslon Text, and even Crimson Text. Both are free.

A little different but still gorgeous, and free, Junicode