Gas/Plasma/Ion Torch locations?

[Malevolent King]

Hey all, I read a game faq that said the plasma torch was back in Mission 4 but now I'm on Mission 7, is it too late to go back and get it? Also I read further that in Mission 8 you get the gas torch and conflicting game faqs are telling me I can upgrade the gas torch to be ion and plasma which conflicts with what I read in the other faq..... so... understandably I'm just a little bit confused. If anyone can clarify, that would be greatly appreciated.

[Simon Knight]

You get each of the torches right before you need them so you won't pass them by.

[Malevolent King]

I missed the plasma torch... so it is possible