Sadly, DVD Architect 7 is now a discontinued product and is no longer available for sale from MAGIX. Please also note that it was never sold (to my knowledge) as a separate product but was part of a purchase of Vegas Pro up to version 17 if memory serves me right (maybe it was 16).

With that in mind, you could search reputable websites selling Vegas Pro 14 up to 17 (or maybe 16) and purchase an older version of Vegas Pro making sure of course that it ships with DVD Architect.

BTW, I'm not sure where you got a "trial" version of DVDA7 from because, as mentioned above, MAGIX no longer sell it, and a trial version of DVDA7 would have only been accessible from a trial version of an old version of Vegas Pro none of which are now available via MAGIX.

Just as a caution, be very careful about buying old versions of Vegas Pro on line - many are scams and/or selling pirated versions with useless serial numbers.

@Dexcon Yes it was once sold as a separate product. It was my first Vegas purchase a few years ago. Towards the end of its sales life it was somewhat hidden away on the Vegas web pages.

This screenshot is from (MAGIX) vegascreativesoftware.com Aug.2017 (from Wayback Machine) re VEGAS DVD A 7. MAGIX sold it separately as @EricLNZ also says.

MAGIX dropped the (VPro 17 and VMSP 17) bundled DVD A 7 early August 2020 when VPro 18 was released and the DVD A 7 product page disappeared then as well. MAGIX stopped selling the separate product later in 2020. (You could ask MAGIX Sales for a while after Aug. '20 if you wanted it.)

Sony DVD Architect was sold also as a separate product even by SCS in their last year. See this comment.