Most buttons are .tga format sheets and gimp (free) will open them and then you can cut out the button and paste it to a new sheet and save as a .png (good quality for web) or .jpg (fair quality) or .gif (crap quality but can animate with GIF editor)
Let me know what buttons you want an I or someone here will tell you what sheet they are on.
ZombiesRus tutorial on adding a button which may help you reverse.
I also did some bonus fixes but please save the images and upload to the wiki or wherever not to overload my image page with hits. https://forums.sinsofasolarempire.com/392969