Well, it's very easy to rule out the first option (since “entrys” is not a word).
Let's forget the prepositional phrase (“of N word-to-be-decided”) for now. How would you phrase the sentence with varying numbers?
“0 entry selected” or “0 entries selected”?
(Ignoring that many style guides will tell you spell out the numeral), the latter is correct.
“1 entry selected" or “1 entries selected”?
As with the last example, this one is pretty clear; the former is correct. Every number beyond one (since it will be plural and will require agreement) will be correct with “entries.”
All right, let's add back the prepositional phrase now. Which would be correct?
“0 of 1 entry selected“ or “0 of 1 entries selected”?
Unlike before, the former is correct. There is only one entry and “entry” must agree with the number in the prepositional phrase. (Note that if you expanded the sentence with a state-of-being verb, it would still be pluralized to agree with zero: “0 of 1 entry are selected.”)
This means that “entry” would be used whenever the number of available entries is one and “entries” should be used otherwise.
As a result, there is no way to add a basic pluralization in parentheses and have it function for all cases. (Though some computer science-minded folk might recommend “1 of 1 entr{y,ies} selected”, it is not common practice.)
Tl;Dr: Neither is correct; You should use “entry” when the available number of entries is one, else use “entries”