No, you literally cannot. Synthesizing a stretch of DNA is trivial, and what you can send away for [1].

Building a functional virus is not even remotely a turn-key operation. Assuming you could get the genome, expressing that genome in a way that results in infectious virus is non-trivial.

[1] Even then, the companies will rarely give you long enough reads to make a full genome scaffold. It looks like there are two companies that will do 50-100kb assemblies as a service today, but I guarantee you they're going to look at what you're trying to make, and who is asking them to do it.