I would love to have a decent looking uniform like that. Nice clean lines. In regards to the helmet, there are a couple of "retro" space helmets around but nothing really eye-catching.
If you want something with the same kind of "silhouette" to that jacket there is https://www.daz3d.com/aftermath-the-admiral
, https://www.daz3d.com/time-soldier-outfit-for-genesis-8-male-s
or https://www.daz3d.com/medieval-prince-outfit-for-genesis-3-male-s
. But I don't think any of them are ideal.
[It seems your post doesn't go through when you put too many hotlinks in]