There's a CMR group for longcasts which should have all the courses (excepting unit specific ones) on it. Download it as a spreadsheet and you can then search / filter down to what you're looking for.
This then usually gets distilled down into specific documents for specialisations / national training which should also be available via DGW.
That said this only applies to Maritime Reserve courses, regular courses are on JPA so you need to go via a PSI. Oh and the secret courses, STC, underwater knife fighting etc clearly aren't available via DGW.