Your third sentence is grammatically correct, but I'm assuming it doesn't have your intended meaning. You probably mean "We won't be able to get an opportunity like this again." Because you're talking about the future, if you use the present tense "can't" ("cannot"), the "can't" doesn't refer to the future but to right now. Specifically, in this case, it changes the meaning of "can't" from the usual meaning "not able to" to a more hyperbolic meaning "it would have grave consequences". That is, "If I want X, I can't do/have Y." "I can't give that guy my phone number." (because he seems bad and might track me down and hurt me) "I can't give up." (because then I'd be a quitter) "I can't say no to ice cream." (because I love eating it, so I'm not going to say no even though I could) vs. "I can't tie my shoes." (because I don't know how, I literally don't have the ability) EX1 "I can't let my daughter go to that party on Saturday." EX2 "I won't let me daughter go to that party on Saturday." EX1 means if the parent let's the daughter go to the party, something bad will probably happen, and the parent doesn't want to feel responsible. It basically means by letting her go, she would be a bad parent. eg. "If I want to be a proper parent (in general), I can't let my daughter do these kinds of things." EX2 means when Saturday comes, the daughter will not be allowed to go (by the parent) because "won't" is future tense, she is saying something that she will do (or not do in this case) in the future. So, using "can't" in your example means something like, "If we get an opportunity like this again, it would be devastating." Opportunities are usually good, so the listener would probably understand that's not the intended meaning. However, a speaker could mean don't want any more opportunities because they (we) keep messing them up and it's becoming stressful. So you want to use, "We won't get an..." or "We won't have an..." or "We won't be able to get an..."

The middle one is perfectly normal and implies people in general don't get these kinds of opportunities every day (on a regular basis). The first and third are grammatically valid but they sound slightly off to me. "I don't always get an opportunity like this." is a little ambiguous and is different from "I/you don't get an opportunity like this every day.", because in the "every day" example, the reader assumes only one opportunity would come on one day, so singular feels right. When you use "always" it refers to a lifetime, so presumably more than one opportunity. The "like this" in this sentence is supposed to be is saying, "like what has happened in this situation" ("like how I just got one"), which is how your second example reads. In your first example, it feels as though "an opportunity like this" is pointing to a specific situation that you've been in and not gotten some opportunity to do something. For example, if you're a copilot and the pilot asks you to land the plane for the first time, a specific opportunity you don't usually get. If you want it to say that you don't get many or any opportunities (in general), use the plural "opportunities like this" (any opportunities such as this opportunity) and change "always" to "usually". "I don't usually get opportunities like this." ( = "I don't usually get any opportunities like this.") This sentence is more clear than your version (assuming this is actually what you meant) and means the same as your second sentence, except that you're talking about yourself instead of people in general. Your version is fine and could also mean this but, as I said, it could also mean a specific opportunity ("like this opportunity right here"). The plural in this case is for the implied "any", and in English you need to pluralize for none or zero or not any. "I have a meeting this morning." "I don't have any meetings this morning." I've run out of room so I'll address the third sentence in it's own post.

Yes