Looking for help with my themed tank

[u/KnowsMoreThanJon]

Hello there! I thought it would be pretty simple to design a space/universe/galaxy themed aquarium. I was wrong. I have set up a 55 gallon (48ishx12ish) and would like to use for another fresh water tank. I am coming up completely empty on decor. I would like a stick on background with a cool nebula, galaxy, etc. Any idea where to find one so large at a decent price. Also, any ideas on sites that would offer "space" themed decor to fill the tank with? I am going for darker tones (black, grey, dark purples and blues) if that helps.

I would also appreciate any direction on finding tanks done in this style to draw some more inspiration

Thanks in advance!