Custom boards for Eclipse
1. Where would I find original graphics to modify?


You could use a scanner. Many home and office printers can act as a scanner, so it should be pretty easy to get access to one. 300dpi is sufficient, but avoid anything lower.

In this particular case, you could derive from this.


  2. How can I produce good quality boards?


Depends on what material you want it printed. If you just want some thick paper, talk to your local print shop.


  3. Is this legal?


The original board does get some Copyright protections.

This doesn't mean what you're doing is illegal. Fair use allows the use of works protected by Copyright. In the US, judges consider the following four factors to determine if a copyrighted work is allowed under by fair use:


The purpose and character of your use,
The nature of the copyrighted work,
The amount and substantiality of the portion taken, and
The effect of the use upon the potential market.


Your custom boards are not a replacement for the game, so the tests lean in your favour.

And if you're doing this for yourself and maybe a few friends, there's really no issue. 

Using Picard's picture is more questionable. But even if it's technically infringing, it's not really a problem unless you start producing many and/or selling them.