Even I've tried to find references and failed. I can share my personal experience here, though, assuming the OP is a fellow Indian.
"Country fellow" is a slightly offensive phrase in south India. It is merely a direct translation of the words from south Indian languages (Malayalam, Tamil, etc.), for example, "naadan chekkan" in Malayalam.
It has nothing to do with the original meaning of fellow countrymen. What it actually means is a person who is cultureless; or someone not trendy enough (among a group of friends, mostly).
Suppose three friends are discussing western music (say, a rap song by Eminem). If one of them tells that he likes Indian carnatic music more, then the other two might say "Oh, grow up! Don't be such a country fellow".
I hope my explanation is clear. I couldn't find any reliable reference to add here. Perhaps it's enough that searching "country fellows" on google will have results related to south Indian slang.
It can also mean "people from the countryside", but that doesn't usually apply when used among friends.
The sucker here has a much longer history than some would have you believe. Basically, sucker punch derives from one of the meanings of the word sucker (NOAD):
sucker 2 informal a gullible or easily deceived person.
Therefore, a "sucker" would be easy to fool with a surprise punch. Etymonline dates the use of the term to 1836, and it appears to derive from the expression for a young mammal before it is weaned, i.e. one that is still sucking at its mother's teat.
Note that despite what Thursagen states, Etymonline also gives different dates for the term suckerpunch:
suckerpunch (n.)
also sucker punch, 1926, from sucker + punch. Figurative use by 1929. As a verb by 1942. Related: Sucker-punched.
Best Answer
I could be mistaken, but I believe this exact phrase originated on Slashdot, in an April Fools' prank on April 1, 2006.
From the Wikipedia page on Slashdot:
The exact Slashdot article said this:
There was a stream of articles on the site that all followed this theme of writing, using lots of caps and texting phrases like LOL, OMG, lots of exclamation points, and getting excited about things like My Little Pony, glitter, the O.C., and other things young girls would be interested in.
Here is the Slashdot site logo from that day:
The meaning of the joke is that this is how young girls write things. So, this phrase is used as a way to jokingly react like a 12-year old girl would.